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 $141.46   6.168%   $150.1853   $150.19   $150.20   $150.20  
  Purchase #2 $32.46   10.122%   $35.7456   $35.75   $35.75   $35.70  
  Purchase #3 $229.62   6.471%   $244.4787   $244.48   $244.50   $244.50  
  Purchase #4 $186.66   8.174%   $201.9176   $201.92   $201.90   $201.90  
  Purchase #5 $58.85   9.719%   $64.5696   $64.57   $64.55   $64.60  
  Purchase #6 $248.97   5.340%   $262.265   $262.27   $262.25   $262.30  
  Purchase #7 $33.64   11.107%   $37.3764   $37.38   $37.40   $37.40  
  7 purchase totals = $931.66       $996.5382   $996.56   $996.55   $996.60