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	$90.96	13.109%	$102.8839	$102.88	$102.90	$102.90
Purchase #2	$235.38	7.407%	$252.8146	$252.81	$252.80	$252.80
Purchase #3	$169.34	12.165%	$189.9402	$189.94	$189.95	$189.90
Purchase #4	$56.35	6.530%	$60.0297	$60.03	$60.05	$60.00
Purchase #5	$146.77	6.821%	$156.7812	$156.78	$156.80	$156.80
Purchase #6	$37.80	7.507%	$40.6376	$40.64	$40.65	$40.60
Purchase #7	$178.34	11.788%	$199.3627	$199.36	$199.35	$199.40
7 purchase totals =	$914.94		$1,002.4499	$1,002.44	$1,002.50	$1,002.40