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 $114.82   9.457%   $125.6785   $125.68   $125.70   $125.70  
  Purchase #2 $143.89   8.861%   $156.6401   $156.64   $156.65   $156.60  
  Purchase #3 $227.78   12.244%   $255.6694   $255.67   $255.65   $255.70  
  Purchase #4 $226.94   8.548%   $246.3388   $246.34   $246.35   $246.30  
  Purchase #5 $33.95   10.810%   $37.62   $37.62   $37.60   $37.60  
  Purchase #6 $57.77   9.796%   $63.4291   $63.43   $63.45   $63.40  
  Purchase #7 $103.28   3.614%   $107.0125   $107.01   $107.00   $107.00  
  7 purchase totals = $908.43       $992.3884   $992.39   $992.40   $992.30