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	$240.25	10.136%	$264.6017	$264.60	$264.60	$264.60
Purchase #2	$91.98	12.638%	$103.6044	$103.60	$103.60	$103.60
Purchase #3	$81.76	8.859%	$89.0031	$89.00	$89.00	$89.00
Purchase #4	$77.31	7.535%	$83.1353	$83.14	$83.15	$83.10
Purchase #5	$236.73	13.813%	$269.4295	$269.43	$269.45	$269.40
Purchase #6	$192.58	11.363%	$214.4629	$214.46	$214.45	$214.50
Purchase #7	$181.90	12.667%	$204.9413	$204.94	$204.95	$204.90
7 purchase totals =	$1,102.51		$1,229.1782	$1,229.17	$1,229.20	$1,229.10