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 $83.72   10.817%   $92.776   $92.78   $92.80   $92.80  
  Purchase #2 $200.52   6.768%   $214.0912   $214.09   $214.10   $214.10  
  Purchase #3 $125.38   5.617%   $132.4226   $132.42   $132.40   $132.40  
  Purchase #4 $23.38   6.821%   $24.9747   $24.97   $24.95   $25.00  
  Purchase #5 $175.35   6.404%   $186.5794   $186.58   $186.60   $186.60  
  Purchase #6 $19.89   6.340%   $21.151   $21.15   $21.15   $21.20  
  Purchase #7 $69.74   9.135%   $76.1107   $76.11   $76.10   $76.10  
  7 purchase totals = $697.98       $748.1056   $748.10   $748.10   $748.20