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 $245.66   9.201%   $268.2632   $268.26   $268.25   $268.30  
  Purchase #2 $157.40   3.346%   $162.6666   $162.67   $162.65   $162.70  
  Purchase #3 $82.28   11.199%   $91.4945   $91.49   $91.50   $91.50  
  Purchase #4 $226.56   9.237%   $247.4873   $247.49   $247.50   $247.50  
  Purchase #5 $130.66   13.446%   $148.2285   $148.23   $148.25   $148.20  
  Purchase #6 $48.49   7.678%   $52.2131   $52.21   $52.20   $52.20  
  Purchase #7 $8.82   6.378%   $9.3825   $9.38   $9.40   $9.40  
  7 purchase totals = $899.87       $979.7357   $979.73   $979.75   $979.80