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 $116.68   6.542%   $124.3132   $124.31   $124.30   $124.30  
  Purchase #2 $32.40   9.644%   $35.5247   $35.52   $35.50   $35.50  
  Purchase #3 $174.98   6.865%   $186.9924   $186.99   $187.00   $187.00  
  Purchase #4 $58.44   6.416%   $62.1895   $62.19   $62.20   $62.20  
  Purchase #5 $210.51   6.513%   $224.2205   $224.22   $224.20   $224.20  
  Purchase #6 $33.95   10.544%   $37.5297   $37.53   $37.55   $37.50  
  Purchase #7 $76.39   10.646%   $84.5225   $84.52   $84.50   $84.50  
  7 purchase totals = $703.35       $755.2925   $755.28   $755.25   $755.20