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 $34.43   8.788%   $37.4557   $37.46   $37.45   $37.50  
  Purchase #2 $128.41   3.138%   $132.4395   $132.44   $132.45   $132.40  
  Purchase #3 $92.96   7.267%   $99.7154   $99.72   $99.70   $99.70  
  Purchase #4 $211.47   11.368%   $235.5099   $235.51   $235.50   $235.50  
  Purchase #5 $58.90   5.397%   $62.0788   $62.08   $62.10   $62.10  
  Purchase #6 $45.67   7.527%   $49.1076   $49.11   $49.10   $49.10  
  Purchase #7 $217.63   9.321%   $237.9153   $237.92   $237.90   $237.90  
  7 purchase totals = $789.47       $854.2222   $854.24   $854.20   $854.20