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 $182.61   5.854%   $193.3   $193.30   $193.30   $193.30  
  Purchase #2 $95.47   3.835%   $99.1313   $99.13   $99.15   $99.10  
  Purchase #3 $223.54   5.742%   $236.3757   $236.38   $236.40   $236.40  
  Purchase #4 $75.35   3.513%   $77.997   $78.00   $78.00   $78.00  
  Purchase #5 $26.93   8.529%   $29.2269   $29.23   $29.25   $29.20  
  Purchase #6 $104.86   3.391%   $108.4158   $108.42   $108.40   $108.40  
  Purchase #7 $19.75   13.490%   $22.4143   $22.41   $22.40   $22.40  
  7 purchase totals = $728.51       $766.8610   $766.87   $766.90   $766.80