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 $207.77   12.629%   $234.0093   $234.01   $234.00   $234.00  
  Purchase #2 $195.50   10.487%   $216.0021   $216.00   $216.00   $216.00  
  Purchase #3 $37.92   7.484%   $40.7579   $40.76   $40.75   $40.80  
  Purchase #4 $151.54   3.835%   $157.3516   $157.35   $157.35   $157.40  
  Purchase #5 $13.36   4.632%   $13.9788   $13.98   $14.00   $14.00  
  Purchase #6 $64.44   13.666%   $73.2464   $73.25   $73.25   $73.20  
  Purchase #7 $107.82   10.463%   $119.1012   $119.10   $119.10   $119.10  
  7 purchase totals = $778.35       $854.4473   $854.45   $854.45   $854.50