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 $67.74   11.707%   $75.6703   $75.67   $75.65   $75.70  
  Purchase #2 $57.48   9.315%   $62.8343   $62.83   $62.85   $62.80  
  Purchase #3 $119.49   12.154%   $134.0128   $134.01   $134.00   $134.00  
  Purchase #4 $199.67   4.412%   $208.4794   $208.48   $208.50   $208.50  
  Purchase #5 $203.62   9.159%   $222.2696   $222.27   $222.25   $222.30  
  Purchase #6 $92.76   7.660%   $99.8654   $99.87   $99.85   $99.90  
  Purchase #7 $38.92   9.198%   $42.4999   $42.50   $42.50   $42.50  
  7 purchase totals = $779.68       $845.6317   $845.63   $845.60   $845.70