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 $208.68   11.819%   $233.3439   $233.34   $233.35   $233.30  
  Purchase #2 $99.39   11.713%   $111.0316   $111.03   $111.05   $111.00  
  Purchase #3 $249.48   10.433%   $275.5082   $275.51   $275.50   $275.50  
  Purchase #4 $72.65   3.724%   $75.3555   $75.36   $75.35   $75.40  
  Purchase #5 $224.65   10.166%   $247.4879   $247.49   $247.50   $247.50  
  Purchase #6 $162.87   8.652%   $176.9615   $176.96   $176.95   $177.00  
  Purchase #7 $196.73   11.710%   $219.7671   $219.77   $219.75   $219.80  
  7 purchase totals = $1,214.45       $1,339.4557   $1,339.46   $1,339.45   $1,339.50