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	$172.79	6.489%	$184.0023	$184.00	$184.00	$184.00
Purchase #2	$144.95	4.663%	$151.709	$151.71	$151.70	$151.70
Purchase #3	$74.64	9.367%	$81.6315	$81.63	$81.65	$81.60
Purchase #4	$28.89	8.696%	$31.4023	$31.40	$31.40	$31.40
Purchase #5	$59.46	9.530%	$65.1265	$65.13	$65.15	$65.10
Purchase #6	$122.55	7.607%	$131.8724	$131.87	$131.85	$131.90
Purchase #7	$147.26	11.672%	$164.4482	$164.45	$164.45	$164.40
7 purchase totals =	$750.54		$810.1922	$810.19	$810.20	$810.10