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 $94.67   12.131%   $106.1544   $106.15   $106.15   $106.20  
  Purchase #2 $158.50   11.624%   $176.924   $176.92   $176.90   $176.90  
  Purchase #3 $44.86   10.684%   $49.6528   $49.65   $49.65   $49.70  
  Purchase #4 $245.85   4.540%   $257.0116   $257.01   $257.00   $257.00  
  Purchase #5 $193.66   5.286%   $203.8969   $203.90   $203.90   $203.90  
  Purchase #6 $210.70   5.115%   $221.4773   $221.48   $221.50   $221.50  
  Purchase #7 $11.51   11.368%   $12.8185   $12.82   $12.80   $12.80  
  7 purchase totals = $959.75       $1,027.9355   $1,027.93   $1,027.90   $1,028.00