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 $225.91   11.681%   $252.2985   $252.30   $252.30   $252.30  
  Purchase #2 $126.74   12.642%   $142.7625   $142.76   $142.75   $142.80  
  Purchase #3 $229.70   12.707%   $258.888   $258.89   $258.90   $258.90  
  Purchase #4 $237.46   13.539%   $269.6097   $269.61   $269.60   $269.60  
  Purchase #5 $61.64   13.404%   $69.9022   $69.90   $69.90   $69.90  
  Purchase #6 $130.64   11.179%   $145.2442   $145.24   $145.25   $145.20  
  Purchase #7 $67.26   12.230%   $75.4859   $75.49   $75.50   $75.50  
  7 purchase totals = $1,079.35       $1,214.1910   $1,214.19   $1,214.20   $1,214.20