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 $75.76   9.508%   $82.9633   $82.96   $82.95   $83.00  
  Purchase #2 $202.39   7.216%   $216.9945   $216.99   $217.00   $217.00  
  Purchase #3 $66.90   10.712%   $74.0663   $74.07   $74.05   $74.10  
  Purchase #4 $141.36   4.867%   $148.24   $148.24   $148.25   $148.20  
  Purchase #5 $181.70   4.624%   $190.1018   $190.10   $190.10   $190.10  
  Purchase #6 $120.38   10.252%   $132.7214   $132.72   $132.70   $132.70  
  Purchase #7 $30.45   7.153%   $32.6281   $32.63   $32.65   $32.60  
  7 purchase totals = $818.94       $877.7154   $877.71   $877.70   $877.70