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 $55.83   4.838%   $58.5311   $58.53   $58.55   $58.50  
  Purchase #2 $141.55   3.711%   $146.8029   $146.80   $146.80   $146.80  
  Purchase #3 $200.86   8.117%   $217.1638   $217.16   $217.15   $217.20  
  Purchase #4 $182.96   9.568%   $200.4656   $200.47   $200.45   $200.50  
  Purchase #5 $184.50   11.316%   $205.378   $205.38   $205.40   $205.40  
  Purchase #6 $83.62   5.843%   $88.5059   $88.51   $88.50   $88.50  
  Purchase #7 $87.89   10.431%   $97.0578   $97.06   $97.05   $97.10  
  7 purchase totals = $937.21       $1,013.9051   $1,013.91   $1,013.90   $1,014.00