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	$83.74	8.553%	$90.9023	$90.90	$90.90	$90.90
Purchase #2	$233.38	9.295%	$255.0727	$255.07	$255.05	$255.10
Purchase #3	$236.37	9.394%	$258.5746	$258.57	$258.55	$258.60
Purchase #4	$247.62	5.266%	$260.6597	$260.66	$260.65	$260.70
Purchase #5	$124.83	4.299%	$130.1964	$130.20	$130.20	$130.20
Purchase #6	$43.85	3.183%	$45.2457	$45.25	$45.25	$45.20
Purchase #7	$130.76	11.834%	$146.2341	$146.23	$146.25	$146.20
7 purchase totals =	$1,100.55		$1,186.8855	$1,186.88	$1,186.85	$1,186.90