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 $63.35   8.462%   $68.7107   $68.71   $68.70   $68.70  
  Purchase #2 $101.67   6.560%   $108.3396   $108.34   $108.35   $108.30  
  Purchase #3 $168.97   12.800%   $190.5982   $190.60   $190.60   $190.60  
  Purchase #4 $34.48   3.782%   $35.784   $35.78   $35.80   $35.80  
  Purchase #5 $241.84   3.822%   $251.0831   $251.08   $251.10   $251.10  
  Purchase #6 $141.79   13.776%   $161.323   $161.32   $161.30   $161.30  
  Purchase #7 $95.31   7.461%   $102.4211   $102.42   $102.40   $102.40  
  7 purchase totals = $847.41       $918.2597   $918.25   $918.25   $918.20