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	$99.82	6.852%	$106.6597	$106.66	$106.65	$106.70
Purchase #2	$77.35	7.442%	$83.1064	$83.11	$83.10	$83.10
Purchase #3	$137.93	3.290%	$142.4679	$142.47	$142.45	$142.50
Purchase #4	$175.36	9.409%	$191.8596	$191.86	$191.85	$191.90
Purchase #5	$66.37	8.559%	$72.0506	$72.05	$72.05	$72.10
Purchase #6	$56.86	6.499%	$60.5553	$60.56	$60.55	$60.60
Purchase #7	$187.69	11.844%	$209.92	$209.92	$209.90	$209.90
7 purchase totals =	$801.38		$866.6195	$866.63	$866.55	$866.80