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 $211.87   11.785%   $236.8389   $236.84   $236.85   $236.80  
  Purchase #2 $35.65   10.196%   $39.2849   $39.28   $39.30   $39.30  
  Purchase #3 $99.83   11.167%   $110.978   $110.98   $111.00   $111.00  
  Purchase #4 $196.99   8.625%   $213.9804   $213.98   $214.00   $214.00  
  Purchase #5 $215.69   12.210%   $242.0257   $242.03   $242.05   $242.00  
  Purchase #6 $72.68   3.872%   $75.4942   $75.49   $75.50   $75.50  
  Purchase #7 $160.37   11.487%   $178.7917   $178.79   $178.80   $178.80  
  7 purchase totals = $993.08       $1,097.3938   $1,097.39   $1,097.50   $1,097.40