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 $241.62   7.205%   $259.0287   $259.03   $259.05   $259.00  
  Purchase #2 $28.52   12.634%   $32.1232   $32.12   $32.10   $32.10  
  Purchase #3 $211.76   11.193%   $235.4623   $235.46   $235.45   $235.50  
  Purchase #4 $173.50   5.149%   $182.4335   $182.43   $182.45   $182.40  
  Purchase #5 $121.48   8.452%   $131.7475   $131.75   $131.75   $131.70  
  Purchase #6 $140.92   5.842%   $149.1525   $149.15   $149.15   $149.20  
  Purchase #7 $11.36   9.769%   $12.4698   $12.47   $12.45   $12.50  
  7 purchase totals = $929.16       $1,002.4175   $1,002.41   $1,002.40   $1,002.40