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	$222.77	7.847%	$240.2508	$240.25	$240.25	$240.30
Purchase #2	$174.66	3.526%	$180.8185	$180.82	$180.80	$180.80
Purchase #3	$55.58	3.673%	$57.6215	$57.62	$57.60	$57.60
Purchase #4	$61.72	6.707%	$65.8596	$65.86	$65.85	$65.90
Purchase #5	$230.37	10.137%	$253.7226	$253.72	$253.70	$253.70
Purchase #6	$28.29	13.463%	$32.0987	$32.10	$32.10	$32.10
Purchase #7	$25.86	6.251%	$27.4765	$27.48	$27.50	$27.50
7 purchase totals =	$799.25		$857.8482	$857.85	$857.80	$857.90