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 $58.95   6.144%   $62.5719   $62.57   $62.55   $62.60  
  Purchase #2 $227.51   13.484%   $258.1874   $258.19   $258.20   $258.20  
  Purchase #3 $148.74   13.807%   $169.2765   $169.28   $169.30   $169.30  
  Purchase #4 $79.44   7.174%   $85.139   $85.14   $85.15   $85.10  
  Purchase #5 $92.52   6.689%   $98.7087   $98.71   $98.70   $98.70  
  Purchase #6 $218.67   11.816%   $244.508   $244.51   $244.50   $244.50  
  Purchase #7 $66.74   11.532%   $74.4365   $74.44   $74.45   $74.40  
  7 purchase totals = $892.57       $992.8280   $992.84   $992.85   $992.80