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 $67.85   8.838%   $73.8466   $73.85   $73.85   $73.80  
  Purchase #2 $228.67   3.503%   $236.6803   $236.68   $236.70   $236.70  
  Purchase #3 $150.98   10.170%   $166.3347   $166.33   $166.35   $166.30  
  Purchase #4 $102.41   5.704%   $108.2515   $108.25   $108.25   $108.30  
  Purchase #5 $14.30   4.329%   $14.919   $14.92   $14.90   $14.90  
  Purchase #6 $142.47   10.429%   $157.3282   $157.33   $157.35   $157.30  
  Purchase #7 $65.49   6.344%   $69.6447   $69.64   $69.65   $69.60  
  7 purchase totals = $772.17       $827.0050   $827.00   $827.05   $826.90