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	$124.72	3.275%	$128.8046	$128.80	$128.80	$128.80
Purchase #2	$141.87	3.148%	$146.3361	$146.34	$146.35	$146.30
Purchase #3	$59.43	13.606%	$67.516	$67.52	$67.50	$67.50
Purchase #4	$231.68	5.546%	$244.529	$244.53	$244.55	$244.50
Purchase #5	$159.43	7.348%	$171.1449	$171.14	$171.15	$171.10
Purchase #6	$9.47	11.390%	$10.5486	$10.55	$10.55	$10.50
Purchase #7	$127.27	13.230%	$144.1078	$144.11	$144.10	$144.10
7 purchase totals =	$853.87		$912.9870	$912.99	$913.00	$912.80