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 $32.62   9.293%   $35.6514   $35.65   $35.65   $35.70  
  Purchase #2 $179.95   8.192%   $194.6915   $194.69   $194.70   $194.70  
  Purchase #3 $34.67   8.738%   $37.6995   $37.70   $37.70   $37.70  
  Purchase #4 $17.62   9.557%   $19.3039   $19.30   $19.30   $19.30  
  Purchase #5 $79.56   13.657%   $90.4255   $90.43   $90.45   $90.40  
  Purchase #6 $153.39   8.645%   $166.6506   $166.65   $166.65   $166.70  
  Purchase #7 $183.94   11.180%   $204.5045   $204.50   $204.50   $204.50  
  7 purchase totals = $681.75       $748.9269   $748.92   $748.95   $749.00