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	$109.42	6.533%	$116.5684	$116.57	$116.55	$116.60
Purchase #2	$231.71	9.524%	$253.7781	$253.78	$253.80	$253.80
Purchase #3	$94.88	5.497%	$100.0956	$100.10	$100.10	$100.10
Purchase #4	$247.50	3.460%	$256.0635	$256.06	$256.05	$256.10
Purchase #5	$74.97	11.853%	$83.8562	$83.86	$83.85	$83.90
Purchase #6	$240.52	5.700%	$254.2296	$254.23	$254.25	$254.20
Purchase #7	$210.33	13.319%	$238.3439	$238.34	$238.35	$238.30
7 purchase totals =	$1,209.33		$1,302.9353	$1,302.94	$1,302.95	$1,303.00