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 $61.39   4.183%   $63.9579   $63.96   $63.95   $64.00  
  Purchase #2 $161.30   6.544%   $171.8555   $171.86   $171.85   $171.90  
  Purchase #3 $51.31   7.674%   $55.2475   $55.25   $55.25   $55.20  
  Purchase #4 $199.26   9.242%   $217.6756   $217.68   $217.70   $217.70  
  Purchase #5 $133.25   8.284%   $144.2884   $144.29   $144.30   $144.30  
  Purchase #6 $91.62   6.231%   $97.3288   $97.33   $97.35   $97.30  
  Purchase #7 $62.90   6.415%   $66.935   $66.94   $66.95   $66.90  
  7 purchase totals = $761.03       $817.2887   $817.31   $817.35   $817.30