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 $66.59   13.743%   $75.7415   $75.74   $75.75   $75.70  
  Purchase #2 $248.81   5.812%   $263.2708   $263.27   $263.25   $263.30  
  Purchase #3 $151.61   7.814%   $163.4568   $163.46   $163.45   $163.50  
  Purchase #4 $55.73   12.623%   $62.7648   $62.76   $62.75   $62.80  
  Purchase #5 $64.97   10.125%   $71.5482   $71.55   $71.55   $71.50  
  Purchase #6 $76.29   10.653%   $84.4172   $84.42   $84.40   $84.40  
  Purchase #7 $217.87   7.860%   $234.9946   $234.99   $235.00   $235.00  
  7 purchase totals = $881.87       $956.1939   $956.19   $956.15   $956.20