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	$54.61	8.834%	$59.4342	$59.43	$59.45	$59.40
Purchase #2	$157.96	10.573%	$174.6611	$174.66	$174.65	$174.70
Purchase #3	$100.38	12.486%	$112.9134	$112.91	$112.90	$112.90
Purchase #4	$145.67	9.201%	$159.0731	$159.07	$159.05	$159.10
Purchase #5	$127.78	7.581%	$137.467	$137.47	$137.45	$137.50
Purchase #6	$61.44	9.751%	$67.431	$67.43	$67.45	$67.40
Purchase #7	$40.26	6.805%	$42.9997	$43.00	$43.00	$43.00
7 purchase totals =	$688.10		$753.9795	$753.97	$753.95	$754.00