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 $113.62   3.794%   $117.9307   $117.93   $117.95   $117.90  
  Purchase #2 $228.47   6.820%   $244.0517   $244.05   $244.05   $244.10  
  Purchase #3 $72.36   6.121%   $76.7892   $76.79   $76.80   $76.80  
  Purchase #4 $183.92   3.220%   $189.8422   $189.84   $189.85   $189.80  
  Purchase #5 $23.96   9.573%   $26.2537   $26.25   $26.25   $26.30  
  Purchase #6 $200.29   5.159%   $210.623   $210.62   $210.60   $210.60  
  Purchase #7 $82.92   13.512%   $94.1242   $94.12   $94.10   $94.10  
  7 purchase totals = $905.54       $959.6147   $959.60   $959.60   $959.60