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	$33.30	13.412%	$37.7662	$37.77	$37.75	$37.80
Purchase #2	$19.91	12.679%	$22.4344	$22.43	$22.45	$22.40
Purchase #3	$216.72	6.740%	$231.3269	$231.33	$231.35	$231.30
Purchase #4	$74.32	12.494%	$83.6055	$83.61	$83.60	$83.60
Purchase #5	$235.47	4.103%	$245.1313	$245.13	$245.15	$245.10
Purchase #6	$75.88	3.568%	$78.5874	$78.59	$78.60	$78.60
Purchase #7	$138.89	8.480%	$150.6679	$150.67	$150.65	$150.70
7 purchase totals =	$794.49		$849.5196	$849.53	$849.55	$849.50