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 $64.78   4.321%   $67.5791   $67.58   $67.60   $67.60  
  Purchase #2 $179.77   6.453%   $191.3706   $191.37   $191.35   $191.40  
  Purchase #3 $144.31   8.597%   $156.7163   $156.72   $156.70   $156.70  
  Purchase #4 $134.31   11.607%   $149.8994   $149.90   $149.90   $149.90  
  Purchase #5 $51.85   11.507%   $57.8164   $57.82   $57.80   $57.80  
  Purchase #6 $118.26   9.301%   $129.2594   $129.26   $129.25   $129.30  
  Purchase #7 $180.71   4.411%   $188.6811   $188.68   $188.70   $188.70  
  7 purchase totals = $873.99       $941.3223   $941.33   $941.30   $941.40