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 $49.94   10.747%   $55.3071   $55.31   $55.30   $55.30  
  Purchase #2 $167.55   13.838%   $190.7356   $190.74   $190.75   $190.70  
  Purchase #3 $43.61   11.528%   $48.6374   $48.64   $48.65   $48.60  
  Purchase #4 $144.78   4.568%   $151.3936   $151.39   $151.40   $151.40  
  Purchase #5 $54.34   4.825%   $56.9619   $56.96   $56.95   $57.00  
  Purchase #6 $114.36   3.216%   $118.0378   $118.04   $118.05   $118.00  
  Purchase #7 $119.92   11.782%   $134.049   $134.05   $134.05   $134.00  
  7 purchase totals = $694.50       $755.1224   $755.13   $755.15   $755.00