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 $247.67   5.487%   $261.2597   $261.26   $261.25   $261.30  
  Purchase #2 $232.41   12.133%   $260.6083   $260.61   $260.60   $260.60  
  Purchase #3 $110.62   8.161%   $119.6477   $119.65   $119.65   $119.60  
  Purchase #4 $208.67   12.308%   $234.3531   $234.35   $234.35   $234.40  
  Purchase #5 $205.45   5.855%   $217.4791   $217.48   $217.50   $217.50  
  Purchase #6 $223.76   4.275%   $233.3257   $233.33   $233.35   $233.30  
  Purchase #7 $235.82   11.777%   $263.5925   $263.59   $263.60   $263.60  
  7 purchase totals = $1,464.40       $1,590.2661   $1,590.27   $1,590.30   $1,590.30