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 $83.35   13.116%   $94.2822   $94.28   $94.30   $94.30  
  Purchase #2 $201.31   11.587%   $224.6358   $224.64   $224.65   $224.60  
  Purchase #3 $201.78   4.628%   $211.1184   $211.12   $211.10   $211.10  
  Purchase #4 $62.41   4.520%   $65.2309   $65.23   $65.25   $65.20  
  Purchase #5 $114.25   4.250%   $119.1056   $119.11   $119.10   $119.10  
  Purchase #6 $80.87   13.406%   $91.7114   $91.71   $91.70   $91.70  
  Purchase #7 $200.62   4.120%   $208.8855   $208.89   $208.90   $208.90  
  7 purchase totals = $944.59       $1,014.9698   $1,014.98   $1,015.00   $1,014.90