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 $89.61   6.783%   $95.6882   $95.69   $95.70   $95.70  
  Purchase #2 $160.76   6.350%   $170.9683   $170.97   $170.95   $171.00  
  Purchase #3 $207.77   5.276%   $218.7319   $218.73   $218.75   $218.70  
  Purchase #4 $52.90   9.568%   $57.9615   $57.96   $57.95   $58.00  
  Purchase #5 $115.46   3.355%   $119.3337   $119.33   $119.35   $119.30  
  Purchase #6 $92.98   11.814%   $103.9647   $103.96   $103.95   $104.00  
  Purchase #7 $106.97   9.495%   $117.1268   $117.13   $117.15   $117.10  
  7 purchase totals = $826.45       $883.7751   $883.77   $883.80   $883.80