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 $195.32   4.444%   $204   $204.00   $204.00   $204.00  
  Purchase #2 $108.78   3.349%   $112.423   $112.42   $112.40   $112.40  
  Purchase #3 $226.57   5.197%   $238.3448   $238.34   $238.35   $238.30  
  Purchase #4 $56.94   9.611%   $62.4125   $62.41   $62.40   $62.40  
  Purchase #5 $53.65   8.815%   $58.3792   $58.38   $58.40   $58.40  
  Purchase #6 $154.76   12.691%   $174.4006   $174.40   $174.40   $174.40  
  Purchase #7 $77.46   7.393%   $83.1866   $83.19   $83.20   $83.20  
  7 purchase totals = $873.48       $933.1467   $933.14   $933.15   $933.10