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	$57.90	11.348%	$64.4705	$64.47	$64.45	$64.50
Purchase #2	$49.26	5.612%	$52.0245	$52.02	$52.00	$52.00
Purchase #3	$50.63	4.468%	$52.8921	$52.89	$52.90	$52.90
Purchase #4	$17.86	5.857%	$18.9061	$18.91	$18.90	$18.90
Purchase #5	$222.63	13.645%	$253.0079	$253.01	$253.00	$253.00
Purchase #6	$23.67	7.599%	$25.4687	$25.47	$25.45	$25.50
Purchase #7	$43.60	4.841%	$45.7107	$45.71	$45.70	$45.70
7 purchase totals =	$465.55		$512.4805	$512.48	$512.40	$512.50