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	$133.54	9.869%	$146.7191	$146.72	$146.70	$146.70
Purchase #2	$80.51	12.659%	$90.7018	$90.70	$90.70	$90.70
Purchase #3	$178.88	4.131%	$186.2695	$186.27	$186.25	$186.30
Purchase #4	$123.74	11.235%	$137.6422	$137.64	$137.65	$137.60
Purchase #5	$87.35	13.663%	$99.2846	$99.28	$99.30	$99.30
Purchase #6	$110.30	9.199%	$120.4465	$120.45	$120.45	$120.40
Purchase #7	$181.33	9.795%	$199.0913	$199.09	$199.10	$199.10
7 purchase totals =	$895.65		$980.1550	$980.15	$980.15	$980.10