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 $110.36   12.623%   $124.2907   $124.29   $124.30   $124.30  
  Purchase #2 $191.55   11.308%   $213.2105   $213.21   $213.20   $213.20  
  Purchase #3 $56.38   7.651%   $60.6936   $60.69   $60.70   $60.70  
  Purchase #4 $246.90   10.704%   $273.3282   $273.33   $273.35   $273.30  
  Purchase #5 $71.93   5.284%   $75.7308   $75.73   $75.75   $75.70  
  Purchase #6 $234.66   7.866%   $253.1184   $253.12   $253.10   $253.10  
  Purchase #7 $180.29   7.866%   $194.4716   $194.47   $194.45   $194.50  
  7 purchase totals = $1,092.07       $1,194.8438   $1,194.84   $1,194.85   $1,194.80