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	$227.73	3.751%	$236.2722	$236.27	$236.25	$236.30
Purchase #2	$71.53	10.207%	$78.8311	$78.83	$78.85	$78.80
Purchase #3	$66.94	10.272%	$73.8161	$73.82	$73.80	$73.80
Purchase #4	$147.90	3.316%	$152.8044	$152.80	$152.80	$152.80
Purchase #5	$10.34	12.762%	$11.6596	$11.66	$11.65	$11.70
Purchase #6	$168.90	8.466%	$183.1991	$183.20	$183.20	$183.20
Purchase #7	$57.88	8.123%	$62.5816	$62.58	$62.60	$62.60
7 purchase totals =	$751.22		$799.1641	$799.16	$799.15	$799.20