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 $228.73   11.322%   $254.6268   $254.63   $254.65   $254.60  
  Purchase #2 $38.97   9.471%   $42.6608   $42.66   $42.65   $42.70  
  Purchase #3 $45.93   4.514%   $48.0033   $48.00   $48.00   $48.00  
  Purchase #4 $232.74   7.371%   $249.8953   $249.90   $249.90   $249.90  
  Purchase #5 $118.70   4.541%   $124.0902   $124.09   $124.10   $124.10  
  Purchase #6 $118.96   12.708%   $134.0774   $134.08   $134.10   $134.10  
  Purchase #7 $201.61   13.711%   $229.2527   $229.25   $229.25   $229.30  
  7 purchase totals = $985.64       $1,082.6065   $1,082.61   $1,082.65   $1,082.70