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	$163.26	5.659%	$172.4989	$172.50	$172.50	$172.50
Purchase #2	$247.69	12.191%	$277.8859	$277.89	$277.90	$277.90
Purchase #3	$250.41	3.116%	$258.2128	$258.21	$258.20	$258.20
Purchase #4	$247.97	7.243%	$265.9305	$265.93	$265.95	$265.90
Purchase #5	$10.94	12.740%	$12.3338	$12.33	$12.35	$12.30
Purchase #6	$34.88	13.369%	$39.5431	$39.54	$39.55	$39.50
Purchase #7	$150.78	7.568%	$162.191	$162.19	$162.20	$162.20
7 purchase totals =	$1,105.93		$1,188.5960	$1,188.59	$1,188.65	$1,188.50