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	$128.27	10.187%	$141.3369	$141.34	$141.35	$141.30
Purchase #2	$42.27	7.651%	$45.5041	$45.50	$45.50	$45.50
Purchase #3	$30.89	8.777%	$33.6012	$33.60	$33.60	$33.60
Purchase #4	$99.47	6.128%	$105.5655	$105.57	$105.55	$105.60
Purchase #5	$50.78	5.412%	$53.5282	$53.53	$53.55	$53.50
Purchase #6	$142.92	3.322%	$147.6678	$147.67	$147.65	$147.70
Purchase #7	$54.44	10.213%	$60	$60.00	$60.00	$60.00
7 purchase totals =	$549.04		$587.2037	$587.21	$587.20	$587.20