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 $188.82   10.662%   $208.952   $208.95   $208.95   $209.00  
  Purchase #2 $104.60   7.782%   $112.74   $112.74   $112.75   $112.70  
  Purchase #3 $49.83   12.273%   $55.9456   $55.95   $55.95   $55.90  
  Purchase #4 $86.93   10.277%   $95.8638   $95.86   $95.85   $95.90  
  Purchase #5 $58.64   10.626%   $64.8711   $64.87   $64.85   $64.90  
  Purchase #6 $175.38   11.753%   $195.9924   $195.99   $196.00   $196.00  
  Purchase #7 $171.78   7.367%   $184.435   $184.44   $184.45   $184.40  
  7 purchase totals = $835.98       $918.7999   $918.80   $918.80   $918.80