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 $23.95   8.262%   $25.9287   $25.93   $25.95   $25.90  
  Purchase #2 $60.50   10.720%   $66.9856   $66.99   $67.00   $67.00  
  Purchase #3 $6.85   11.861%   $7.6625   $7.66   $7.65   $7.70  
  Purchase #4 $229.46   10.548%   $253.6634   $253.66   $253.65   $253.70  
  Purchase #5 $233.51   10.159%   $257.2323   $257.23   $257.25   $257.20  
  Purchase #6 $82.68   13.326%   $93.6979   $93.70   $93.70   $93.70  
  Purchase #7 $43.54   10.146%   $47.9576   $47.96   $47.95   $48.00  
  7 purchase totals = $680.49       $753.1280   $753.13   $753.15   $753.20