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	$91.96	12.593%	$103.5405	$103.54	$103.55	$103.50
Purchase #2	$213.51	5.140%	$224.4844	$224.48	$224.50	$224.50
Purchase #3	$137.36	9.289%	$150.1194	$150.12	$150.10	$150.10
Purchase #4	$167.68	10.378%	$185.0818	$185.08	$185.10	$185.10
Purchase #5	$248.85	3.181%	$256.7659	$256.77	$256.75	$256.80
Purchase #6	$217.76	9.522%	$238.4951	$238.50	$238.50	$238.50
Purchase #7	$145.82	5.448%	$153.7643	$153.76	$153.75	$153.80
7 purchase totals =	$1,222.94		$1,312.2514	$1,312.25	$1,312.25	$1,312.30