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	$84.75	7.577%	$91.1715	$91.17	$91.15	$91.20
Purchase #2	$23.55	8.548%	$25.5631	$25.56	$25.55	$25.60
Purchase #3	$120.26	8.459%	$130.4328	$130.43	$130.45	$130.40
Purchase #4	$117.72	5.155%	$123.7885	$123.79	$123.80	$123.80
Purchase #5	$202.91	9.155%	$221.4864	$221.49	$221.50	$221.50
Purchase #6	$180.82	5.476%	$190.7217	$190.72	$190.70	$190.70
Purchase #7	$34.63	7.783%	$37.3253	$37.33	$37.35	$37.30
7 purchase totals =	$764.64		$820.4893	$820.49	$820.50	$820.50