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 $155.44   11.874%   $173.8969   $173.90   $173.90   $173.90  
  Purchase #2 $131.53   7.642%   $141.5815   $141.58   $141.60   $141.60  
  Purchase #3 $55.29   5.623%   $58.399   $58.40   $58.40   $58.40  
  Purchase #4 $224.67   9.472%   $245.9507   $245.95   $245.95   $246.00  
  Purchase #5 $191.48   9.155%   $209.01   $209.01   $209.00   $209.00  
  Purchase #6 $107.38   5.762%   $113.5672   $113.57   $113.55   $113.60  
  Purchase #7 $11.38   12.290%   $12.7786   $12.78   $12.80   $12.80  
  7 purchase totals = $877.17       $955.1839   $955.19   $955.20   $955.30