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	$233.80	9.857%	$256.8457	$256.85	$256.85	$256.80
Purchase #2	$29.36	12.652%	$33.0746	$33.07	$33.05	$33.10
Purchase #3	$91.75	9.184%	$100.1763	$100.18	$100.20	$100.20
Purchase #4	$73.49	4.850%	$77.0543	$77.05	$77.05	$77.10
Purchase #5	$195.67	7.776%	$210.8853	$210.89	$210.90	$210.90
Purchase #6	$163.36	13.520%	$185.4463	$185.45	$185.45	$185.40
Purchase #7	$51.43	3.192%	$53.0716	$53.07	$53.05	$53.10
7 purchase totals =	$838.86		$916.5541	$916.56	$916.55	$916.60