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 $202.91   5.580%   $214.2324   $214.23   $214.25   $214.20  
  Purchase #2 $199.62   8.181%   $215.9509   $215.95   $215.95   $216.00  
  Purchase #3 $26.82   7.288%   $28.7746   $28.77   $28.75   $28.80  
  Purchase #4 $48.82   10.837%   $54.1106   $54.11   $54.10   $54.10  
  Purchase #5 $99.78   13.420%   $113.1705   $113.17   $113.15   $113.20  
  Purchase #6 $209.26   11.608%   $233.5509   $233.55   $233.55   $233.60  
  Purchase #7 $239.87   6.262%   $254.8907   $254.89   $254.90   $254.90  
  7 purchase totals = $1,027.08       $1,114.6806   $1,114.67   $1,114.65   $1,114.80