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	$20.57	12.447%	$23.1303	$23.13	$23.15	$23.10
Purchase #2	$35.82	5.478%	$37.7822	$37.78	$37.80	$37.80
Purchase #3	$212.60	4.331%	$221.8077	$221.81	$221.80	$221.80
Purchase #4	$105.82	3.690%	$109.7248	$109.72	$109.70	$109.70
Purchase #5	$67.89	8.276%	$73.5086	$73.51	$73.50	$73.50
Purchase #6	$81.53	11.672%	$91.0462	$91.05	$91.05	$91.00
Purchase #7	$51.96	5.420%	$54.7762	$54.78	$54.80	$54.80
7 purchase totals =	$576.19		$611.7760	$611.78	$611.80	$611.70