Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.63   6.433%   $257.1741   $257.17   $257.15   $257.20  
  Purchase #2 $175.34   9.431%   $191.8763   $191.88   $191.90   $191.90  
  Purchase #3 $155.49   13.411%   $176.3428   $176.34   $176.35   $176.30  
  Purchase #4 $210.96   9.804%   $231.6425   $231.64   $231.65   $231.60  
  Purchase #5 $233.67   8.339%   $253.1557   $253.16   $253.15   $253.20  
  Purchase #6 $156.91   10.287%   $173.0513   $173.05   $173.05   $173.10  
  Purchase #7 $181.53   12.102%   $203.4988   $203.50   $203.50   $203.50  
  7 purchase totals = $1,355.53       $1,486.7415   $1,486.74   $1,486.75   $1,486.80