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 $224.89   12.780%   $253.6309   $253.63   $253.65   $253.60  
  Purchase #2 $126.40   12.113%   $141.7108   $141.71   $141.70   $141.70  
  Purchase #3 $137.56   11.854%   $153.8664   $153.87   $153.85   $153.90  
  Purchase #4 $92.65   5.546%   $97.7884   $97.79   $97.80   $97.80  
  Purchase #5 $208.58   9.184%   $227.736   $227.74   $227.75   $227.70  
  Purchase #6 $101.95   4.453%   $106.4898   $106.49   $106.50   $106.50  
  Purchase #7 $221.79   11.815%   $247.9945   $247.99   $248.00   $248.00  
  7 purchase totals = $1,113.82       $1,229.2168   $1,229.22   $1,229.25   $1,229.20