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 $37.83   7.798%   $40.78   $40.78   $40.80   $40.80  
  Purchase #2 $213.55   7.490%   $229.5449   $229.54   $229.55   $229.50  
  Purchase #3 $194.45   13.202%   $220.1213   $220.12   $220.10   $220.10  
  Purchase #4 $153.75   5.241%   $161.808   $161.81   $161.80   $161.80  
  Purchase #5 $154.60   13.321%   $175.1943   $175.19   $175.20   $175.20  
  Purchase #6 $24.42   6.388%   $25.9799   $25.98   $26.00   $26.00  
  Purchase #7 $14.74   5.500%   $15.5507   $15.55   $15.55   $15.60  
  7 purchase totals = $793.34       $868.9791   $868.97   $869.00   $869.00