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	$243.53	8.420%	$264.0352	$264.04	$264.05	$264.00
Purchase #2	$175.60	11.712%	$196.1663	$196.17	$196.15	$196.20
Purchase #3	$58.75	9.385%	$64.2637	$64.26	$64.25	$64.30
Purchase #4	$16.80	4.520%	$17.5594	$17.56	$17.55	$17.60
Purchase #5	$31.40	4.741%	$32.8887	$32.89	$32.90	$32.90
Purchase #6	$140.44	5.272%	$147.844	$147.84	$147.85	$147.80
Purchase #7	$184.93	8.559%	$200.7582	$200.76	$200.75	$200.80
7 purchase totals =	$851.45		$923.5155	$923.52	$923.50	$923.60