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	$234.50	8.282%	$253.9213	$253.92	$253.90	$253.90
Purchase #2	$149.63	10.612%	$165.5087	$165.51	$165.50	$165.50
Purchase #3	$35.84	4.562%	$37.475	$37.48	$37.50	$37.50
Purchase #4	$215.91	5.304%	$227.3619	$227.36	$227.35	$227.40
Purchase #5	$184.72	11.328%	$205.6451	$205.65	$205.65	$205.60
Purchase #6	$164.93	4.314%	$172.0451	$172.05	$172.05	$172.00
Purchase #7	$237.59	5.243%	$250.0468	$250.05	$250.05	$250.00
7 purchase totals =	$1,223.12		$1,312.0039	$1,312.02	$1,312.00	$1,311.90