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 $90.63   13.460%   $102.8288   $102.83   $102.85   $102.80  
  Purchase #2 $165.38   4.844%   $173.391   $173.39   $173.40   $173.40  
  Purchase #3 $73.56   5.494%   $77.6014   $77.60   $77.60   $77.60  
  Purchase #4 $219.53   11.679%   $245.1689   $245.17   $245.15   $245.20  
  Purchase #5 $185.31   11.777%   $207.134   $207.13   $207.15   $207.10  
  Purchase #6 $60.66   9.257%   $66.2753   $66.28   $66.30   $66.30  
  Purchase #7 $10.66   8.479%   $11.5639   $11.56   $11.55   $11.60  
  7 purchase totals = $805.73       $883.9633   $883.96   $884.00   $884.00