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 $97.85   3.331%   $101.1094   $101.11   $101.10   $101.10  
  Purchase #2 $59.62   10.112%   $65.6488   $65.65   $65.65   $65.60  
  Purchase #3 $200.78   5.144%   $211.1081   $211.11   $211.10   $211.10  
  Purchase #4 $104.71   9.128%   $114.2679   $114.27   $114.25   $114.30  
  Purchase #5 $50.96   9.412%   $55.7564   $55.76   $55.75   $55.80  
  Purchase #6 $118.63   5.620%   $125.297   $125.30   $125.30   $125.30  
  Purchase #7 $230.33   12.844%   $259.9136   $259.91   $259.90   $259.90  
  7 purchase totals = $862.88       $933.1012   $933.11   $933.05   $933.10