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 $69.46   8.247%   $75.1884   $75.19   $75.20   $75.20  
  Purchase #2 $178.98   13.548%   $203.2282   $203.23   $203.25   $203.20  
  Purchase #3 $204.41   6.735%   $218.177   $218.18   $218.20   $218.20  
  Purchase #4 $238.26   7.715%   $256.6418   $256.64   $256.65   $256.60  
  Purchase #5 $182.61   4.541%   $190.9023   $190.90   $190.90   $190.90  
  Purchase #6 $231.69   5.498%   $244.4283   $244.43   $244.45   $244.40  
  Purchase #7 $243.60   4.242%   $253.9335   $253.93   $253.95   $253.90  
  7 purchase totals = $1,349.01       $1,442.4995   $1,442.50   $1,442.60   $1,442.40