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 $204.49   9.769%   $224.4666   $224.47   $224.45   $224.50  
  Purchase #2 $189.84   13.625%   $215.7057   $215.71   $215.70   $215.70  
  Purchase #3 $239.71   10.513%   $264.9107   $264.91   $264.90   $264.90  
  Purchase #4 $99.29   11.393%   $110.6021   $110.60   $110.60   $110.60  
  Purchase #5 $229.77   6.870%   $245.5552   $245.56   $245.55   $245.60  
  Purchase #6 $60.54   7.315%   $64.9685   $64.97   $64.95   $65.00  
  Purchase #7 $224.51   8.248%   $243.0276   $243.03   $243.05   $243.00  
  7 purchase totals = $1,248.15       $1,369.2364   $1,369.25   $1,369.20   $1,369.30