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 $239.86   6.144%   $254.597   $254.60   $254.60   $254.60  
  Purchase #2 $63.27   9.200%   $69.0908   $69.09   $69.10   $69.10  
  Purchase #3 $15.60   3.581%   $16.1586   $16.16   $16.15   $16.20  
  Purchase #4 $144.91   9.495%   $158.6692   $158.67   $158.65   $158.70  
  Purchase #5 $120.42   3.459%   $124.5853   $124.59   $124.60   $124.60  
  Purchase #6 $214.52   8.576%   $232.9172   $232.92   $232.90   $232.90  
  Purchase #7 $167.63   10.481%   $185.1993   $185.20   $185.20   $185.20  
  7 purchase totals = $966.21       $1,041.2174   $1,041.23   $1,041.20   $1,041.30