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 $108.67   13.722%   $123.5817   $123.58   $123.60   $123.60  
  Purchase #2 $63.56   11.625%   $70.9489   $70.95   $70.95   $70.90  
  Purchase #3 $27.79   12.559%   $31.2801   $31.28   $31.30   $31.30  
  Purchase #4 $27.80   6.112%   $29.4991   $29.50   $29.50   $29.50  
  Purchase #5 $98.80   3.471%   $102.2293   $102.23   $102.25   $102.20  
  Purchase #6 $216.65   13.872%   $246.7037   $246.70   $246.70   $246.70  
  Purchase #7 $182.85   4.128%   $190.398   $190.40   $190.40   $190.40  
  7 purchase totals = $726.12       $794.6408   $794.64   $794.70   $794.60