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 $61.46   6.385%   $65.3842   $65.38   $65.40   $65.40  
  Purchase #2 $48.77   9.792%   $53.5456   $53.55   $53.55   $53.50  
  Purchase #3 $102.26   11.663%   $114.1866   $114.19   $114.20   $114.20  
  Purchase #4 $153.39   10.829%   $170.0006   $170.00   $170.00   $170.00  
  Purchase #5 $195.49   4.151%   $203.6048   $203.60   $203.60   $203.60  
  Purchase #6 $228.43   10.788%   $253.073   $253.07   $253.05   $253.10  
  Purchase #7 $33.93   7.302%   $36.4076   $36.41   $36.40   $36.40  
  7 purchase totals = $823.73       $896.2024   $896.20   $896.20   $896.20