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 $18.87   3.636%   $19.5561   $19.56   $19.55   $19.60  
  Purchase #2 $154.52   3.442%   $159.8386   $159.84   $159.85   $159.80  
  Purchase #3 $156.81   3.539%   $162.3595   $162.36   $162.35   $162.40  
  Purchase #4 $98.25   13.870%   $111.8773   $111.88   $111.90   $111.90  
  Purchase #5 $23.63   12.593%   $26.6057   $26.61   $26.60   $26.60  
  Purchase #6 $19.88   3.313%   $20.5386   $20.54   $20.55   $20.50  
  Purchase #7 $229.90   11.843%   $257.1271   $257.13   $257.15   $257.10  
  7 purchase totals = $701.86       $757.9029   $757.92   $757.95   $757.90