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 $38.88   12.257%   $43.6455   $43.65   $43.65   $43.60  
  Purchase #2 $62.65   8.336%   $67.8725   $67.87   $67.85   $67.90  
  Purchase #3 $103.46   8.780%   $112.5438   $112.54   $112.55   $112.50  
  Purchase #4 $194.98   7.420%   $209.4475   $209.45   $209.45   $209.40  
  Purchase #5 $154.95   10.248%   $170.8293   $170.83   $170.85   $170.80  
  Purchase #6 $198.44   4.811%   $207.9869   $207.99   $208.00   $208.00  
  Purchase #7 $82.86   12.294%   $93.0468   $93.05   $93.05   $93.00  
  7 purchase totals = $836.22       $905.3723   $905.38   $905.40   $905.20