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	$53.68	5.802%	$56.7945	$56.79	$56.80	$56.80
Purchase #2	$92.92	6.784%	$99.2237	$99.22	$99.20	$99.20
Purchase #3	$142.82	6.461%	$152.0476	$152.05	$152.05	$152.00
Purchase #4	$140.52	6.520%	$149.6819	$149.68	$149.70	$149.70
Purchase #5	$67.30	6.175%	$71.4558	$71.46	$71.45	$71.50
Purchase #6	$143.78	12.245%	$161.3859	$161.39	$161.40	$161.40
Purchase #7	$139.76	5.857%	$147.9457	$147.95	$147.95	$147.90
7 purchase totals =	$780.78		$838.5351	$838.54	$838.55	$838.50