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	$235.55	3.774%	$244.4397	$244.44	$244.45	$244.40
Purchase #2	$88.86	13.760%	$101.0871	$101.09	$101.10	$101.10
Purchase #3	$136.50	11.562%	$152.2821	$152.28	$152.30	$152.30
Purchase #4	$94.33	5.828%	$99.8276	$99.83	$99.85	$99.80
Purchase #5	$64.58	3.567%	$66.8836	$66.88	$66.90	$66.90
Purchase #6	$84.26	7.176%	$90.3065	$90.31	$90.30	$90.30
Purchase #7	$19.74	11.675%	$22.0446	$22.04	$22.05	$22.00
7 purchase totals =	$723.82		$776.8712	$776.87	$776.95	$776.80