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 $241.56   11.630%   $269.6534   $269.65   $269.65   $269.70  
  Purchase #2 $148.59   9.254%   $162.3405   $162.34   $162.35   $162.30  
  Purchase #3 $213.70   11.134%   $237.4934   $237.49   $237.50   $237.50  
  Purchase #4 $14.41   11.769%   $16.1059   $16.11   $16.10   $16.10  
  Purchase #5 $65.43   3.776%   $67.9006   $67.90   $67.90   $67.90  
  Purchase #6 $36.96   5.536%   $39.0061   $39.01   $39.00   $39.00  
  Purchase #7 $132.97   13.690%   $151.1736   $151.17   $151.15   $151.20  
  7 purchase totals = $853.62       $943.6735   $943.67   $943.65   $943.70