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 $225.67   3.226%   $232.9501   $232.95   $232.95   $233.00  
  Purchase #2 $69.33   8.252%   $75.0511   $75.05   $75.05   $75.10  
  Purchase #3 $142.63   11.308%   $158.7586   $158.76   $158.75   $158.80  
  Purchase #4 $244.53   9.383%   $267.4742   $267.47   $267.45   $267.50  
  Purchase #5 $57.42   9.527%   $62.8904   $62.89   $62.90   $62.90  
  Purchase #6 $168.39   12.642%   $189.6779   $189.68   $189.70   $189.70  
  Purchase #7 $54.53   4.216%   $56.829   $56.83   $56.85   $56.80  
  7 purchase totals = $962.50       $1,043.6313   $1,043.63   $1,043.65   $1,043.80