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 $24.73   6.684%   $26.383   $26.38   $26.40   $26.40  
  Purchase #2 $211.43   11.524%   $235.7952   $235.80   $235.80   $235.80  
  Purchase #3 $50.95   10.732%   $56.418   $56.42   $56.40   $56.40  
  Purchase #4 $241.28   8.798%   $262.5078   $262.51   $262.50   $262.50  
  Purchase #5 $55.98   5.145%   $58.8602   $58.86   $58.85   $58.90  
  Purchase #6 $199.57   8.427%   $216.3878   $216.39   $216.40   $216.40  
  Purchase #7 $10.94   7.648%   $11.7767   $11.78   $11.80   $11.80  
  7 purchase totals = $794.88       $868.1287   $868.14   $868.15   $868.20