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 $110.97   12.591%   $124.9422   $124.94   $124.95   $124.90  
  Purchase #2 $209.64   13.201%   $237.3146   $237.31   $237.30   $237.30  
  Purchase #3 $194.32   5.686%   $205.369   $205.37   $205.35   $205.40  
  Purchase #4 $15.69   8.322%   $16.9957   $17.00   $17.00   $17.00  
  Purchase #5 $29.66   12.263%   $33.2972   $33.30   $33.30   $33.30  
  Purchase #6 $154.34   5.854%   $163.3751   $163.38   $163.40   $163.40  
  Purchase #7 $232.90   7.533%   $250.4444   $250.44   $250.45   $250.40  
  7 purchase totals = $947.52       $1,031.7382   $1,031.74   $1,031.75   $1,031.70