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 $165.85   13.173%   $187.6974   $187.70   $187.70   $187.70  
  Purchase #2 $135.93   11.586%   $151.6788   $151.68   $151.70   $151.70  
  Purchase #3 $34.98   3.786%   $36.3043   $36.30   $36.30   $36.30  
  Purchase #4 $124.63   11.149%   $138.525   $138.53   $138.55   $138.50  
  Purchase #5 $209.78   8.525%   $227.6637   $227.66   $227.65   $227.70  
  Purchase #6 $58.81   13.763%   $66.904   $66.90   $66.90   $66.90  
  Purchase #7 $44.44   6.127%   $47.1628   $47.16   $47.15   $47.20  
  7 purchase totals = $774.42       $855.9360   $855.93   $855.95   $856.00