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	$40.58	3.809%	$42.1257	$42.13	$42.15	$42.10
Purchase #2	$95.73	13.537%	$108.689	$108.69	$108.70	$108.70
Purchase #3	$29.45	13.172%	$33.3292	$33.33	$33.35	$33.30
Purchase #4	$132.31	7.797%	$142.6262	$142.63	$142.65	$142.60
Purchase #5	$77.60	9.539%	$85.0023	$85.00	$85.00	$85.00
Purchase #6	$172.42	4.107%	$179.5013	$179.50	$179.50	$179.50
Purchase #7	$187.74	3.171%	$193.6932	$193.69	$193.70	$193.70
7 purchase totals =	$735.83		$784.9669	$784.97	$785.05	$784.90