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	$7.63	13.550%	$8.6639	$8.66	$8.65	$8.70
Purchase #2	$174.29	6.330%	$185.3226	$185.32	$185.30	$185.30
Purchase #3	$51.63	10.234%	$56.9138	$56.91	$56.90	$56.90
Purchase #4	$33.31	13.845%	$37.9218	$37.92	$37.90	$37.90
Purchase #5	$114.44	12.845%	$129.1398	$129.14	$129.15	$129.10
Purchase #6	$78.32	4.740%	$82.0324	$82.03	$82.05	$82.00
Purchase #7	$15.68	11.765%	$17.5248	$17.52	$17.50	$17.50
7 purchase totals =	$475.30		$517.5191	$517.50	$517.45	$517.40