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	$168.68	9.400%	$184.5359	$184.54	$184.55	$184.50
Purchase #2	$131.47	4.747%	$137.7109	$137.71	$137.70	$137.70
Purchase #3	$91.98	9.240%	$100.479	$100.48	$100.50	$100.50
Purchase #4	$89.60	6.172%	$95.1301	$95.13	$95.15	$95.10
Purchase #5	$36.59	7.487%	$39.3295	$39.33	$39.35	$39.30
Purchase #6	$49.85	8.159%	$53.9173	$53.92	$53.90	$53.90
Purchase #7	$34.33	7.668%	$36.9624	$36.96	$36.95	$37.00
7 purchase totals =	$602.50		$648.0651	$648.07	$648.10	$648.00