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 $91.54   10.493%   $101.1453   $101.15   $101.15   $101.10  
  Purchase #2 $203.98   10.444%   $225.2837   $225.28   $225.30   $225.30  
  Purchase #3 $244.32   7.231%   $261.9868   $261.99   $262.00   $262.00  
  Purchase #4 $87.99   7.609%   $94.6852   $94.69   $94.70   $94.70  
  Purchase #5 $208.42   8.419%   $225.9669   $225.97   $225.95   $226.00  
  Purchase #6 $51.94   11.168%   $57.7407   $57.74   $57.75   $57.70  
  Purchase #7 $63.68   9.410%   $69.6723   $69.67   $69.65   $69.70  
  7 purchase totals = $951.87       $1,036.4809   $1,036.49   $1,036.50   $1,036.50