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	$227.86	13.410%	$258.416	$258.42	$258.40	$258.40
Purchase #2	$175.36	9.418%	$191.8754	$191.88	$191.90	$191.90
Purchase #3	$246.83	7.597%	$265.5817	$265.58	$265.60	$265.60
Purchase #4	$129.71	8.426%	$140.6394	$140.64	$140.65	$140.60
Purchase #5	$29.39	8.398%	$31.8582	$31.86	$31.85	$31.90
Purchase #6	$85.57	8.559%	$92.8939	$92.89	$92.90	$92.90
Purchase #7	$170.60	12.730%	$192.3174	$192.32	$192.30	$192.30
7 purchase totals =	$1,065.32		$1,173.5820	$1,173.59	$1,173.60	$1,173.60