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	$160.57	13.236%	$181.823	$181.82	$181.80	$181.80
Purchase #2	$136.61	4.313%	$142.502	$142.50	$142.50	$142.50
Purchase #3	$71.43	13.640%	$81.1731	$81.17	$81.15	$81.20
Purchase #4	$176.32	5.288%	$185.6438	$185.64	$185.65	$185.60
Purchase #5	$243.67	10.539%	$269.3504	$269.35	$269.35	$269.40
Purchase #6	$11.52	13.295%	$13.0516	$13.05	$13.05	$13.10
Purchase #7	$52.40	10.188%	$57.7385	$57.74	$57.75	$57.70
7 purchase totals =	$852.52		$931.2824	$931.27	$931.25	$931.30