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 $47.37   8.811%   $51.5438   $51.54   $51.55   $51.50  
  Purchase #2 $61.88   9.610%   $67.8267   $67.83   $67.85   $67.80  
  Purchase #3 $214.62   4.788%   $224.896   $224.90   $224.90   $224.90  
  Purchase #4 $155.92   7.484%   $167.5891   $167.59   $167.60   $167.60  
  Purchase #5 $139.25   5.664%   $147.1371   $147.14   $147.15   $147.10  
  Purchase #6 $58.49   13.173%   $66.1949   $66.19   $66.20   $66.20  
  Purchase #7 $101.79   5.142%   $107.024   $107.02   $107.00   $107.00  
  7 purchase totals = $779.32       $832.2116   $832.21   $832.25   $832.10