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 $61.36   6.281%   $65.214   $65.21   $65.20   $65.20  
  Purchase #2 $97.45   8.512%   $105.7449   $105.74   $105.75   $105.70  
  Purchase #3 $6.43   3.809%   $6.6749   $6.67   $6.65   $6.70  
  Purchase #4 $158.94   11.743%   $177.6043   $177.60   $177.60   $177.60  
  Purchase #5 $149.30   10.639%   $165.184   $165.18   $165.20   $165.20  
  Purchase #6 $159.95   12.811%   $180.4412   $180.44   $180.45   $180.40  
  Purchase #7 $145.50   4.852%   $152.5597   $152.56   $152.55   $152.60  
  7 purchase totals = $778.93       $853.4230   $853.40   $853.40   $853.40