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 $83.95   4.178%   $87.4574   $87.46   $87.45   $87.50  
  Purchase #2 $92.78   8.403%   $100.5763   $100.58   $100.60   $100.60  
  Purchase #3 $11.92   5.327%   $12.555   $12.56   $12.55   $12.60  
  Purchase #4 $152.47   10.782%   $168.9093   $168.91   $168.90   $168.90  
  Purchase #5 $37.91   7.502%   $40.754   $40.75   $40.75   $40.80  
  Purchase #6 $157.73   12.260%   $177.0677   $177.07   $177.05   $177.10  
  Purchase #7 $174.41   4.556%   $182.3561   $182.36   $182.35   $182.40  
  7 purchase totals = $711.17       $769.6758   $769.69   $769.65   $769.90