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	$141.32	3.279%	$145.9539	$145.95	$145.95	$146.00
Purchase #2	$169.90	8.341%	$184.0714	$184.07	$184.05	$184.10
Purchase #3	$67.26	9.205%	$73.4513	$73.45	$73.45	$73.50
Purchase #4	$38.28	11.369%	$42.6321	$42.63	$42.65	$42.60
Purchase #5	$159.39	12.142%	$178.7431	$178.74	$178.75	$178.70
Purchase #6	$238.31	4.668%	$249.4343	$249.43	$249.45	$249.40
Purchase #7	$103.70	7.506%	$111.4837	$111.48	$111.50	$111.50
7 purchase totals =	$918.16		$985.7698	$985.75	$985.80	$985.80