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 $32.95   9.683%   $36.1405   $36.14   $36.15   $36.10  
  Purchase #2 $230.51   8.434%   $249.9512   $249.95   $249.95   $250.00  
  Purchase #3 $247.96   6.532%   $264.1567   $264.16   $264.15   $264.20  
  Purchase #4 $110.34   8.250%   $119.4431   $119.44   $119.45   $119.40  
  Purchase #5 $240.68   7.531%   $258.8056   $258.81   $258.80   $258.80  
  Purchase #6 $135.91   10.655%   $150.3912   $150.39   $150.40   $150.40  
  Purchase #7 $235.36   13.734%   $267.6843   $267.68   $267.70   $267.70  
  7 purchase totals = $1,233.71       $1,346.5726   $1,346.57   $1,346.60   $1,346.60