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 $86.81   13.726%   $98.7255   $98.73   $98.75   $98.70  
  Purchase #2 $25.96   9.861%   $28.5199   $28.52   $28.50   $28.50  
  Purchase #3 $117.31   12.272%   $131.7063   $131.71   $131.70   $131.70  
  Purchase #4 $234.32   12.483%   $263.5702   $263.57   $263.55   $263.60  
  Purchase #5 $111.88   12.185%   $125.5126   $125.51   $125.50   $125.50  
  Purchase #6 $167.82   8.565%   $182.1938   $182.19   $182.20   $182.20  
  Purchase #7 $91.82   3.499%   $95.0328   $95.03   $95.05   $95.00  
  7 purchase totals = $835.92       $925.2611   $925.26   $925.25   $925.20