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	$240.50	3.117%	$247.9964	$248.00	$248.00	$248.00
Purchase #2	$54.86	12.162%	$61.5321	$61.53	$61.55	$61.50
Purchase #3	$96.33	13.314%	$109.1554	$109.16	$109.15	$109.20
Purchase #4	$14.31	13.707%	$16.2715	$16.27	$16.25	$16.30
Purchase #5	$205.51	11.738%	$229.6328	$229.63	$229.65	$229.60
Purchase #6	$69.42	9.415%	$75.9559	$75.96	$75.95	$76.00
Purchase #7	$223.29	6.741%	$238.342	$238.34	$238.35	$238.30
7 purchase totals =	$904.22		$978.8861	$978.89	$978.90	$978.90