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 $86.50   13.339%   $98.0382   $98.04   $98.05   $98.00  
  Purchase #2 $10.96   12.385%   $12.3174   $12.32   $12.30   $12.30  
  Purchase #3 $174.71   3.125%   $180.1697   $180.17   $180.15   $180.20  
  Purchase #4 $248.99   9.829%   $273.4632   $273.46   $273.45   $273.50  
  Purchase #5 $91.88   3.855%   $95.422   $95.42   $95.40   $95.40  
  Purchase #6 $34.25   10.397%   $37.811   $37.81   $37.80   $37.80  
  Purchase #7 $51.98   4.167%   $54.146   $54.15   $54.15   $54.10  
  7 purchase totals = $699.27       $751.3675   $751.37   $751.30   $751.30