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	$95.93	12.820%	$108.2282	$108.23	$108.25	$108.20
Purchase #2	$148.97	4.493%	$155.6632	$155.66	$155.65	$155.70
Purchase #3	$205.76	7.873%	$221.9595	$221.96	$221.95	$222.00
Purchase #4	$190.59	10.120%	$209.8777	$209.88	$209.90	$209.90
Purchase #5	$35.34	5.233%	$37.1893	$37.19	$37.20	$37.20
Purchase #6	$171.49	10.144%	$188.8859	$188.89	$188.90	$188.90
Purchase #7	$9.73	7.493%	$10.4591	$10.46	$10.45	$10.50
7 purchase totals =	$857.81		$932.2629	$932.27	$932.30	$932.40