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	$69.89	12.390%	$78.5494	$78.55	$78.55	$78.50
Purchase #2	$191.65	7.192%	$205.4335	$205.43	$205.45	$205.40
Purchase #3	$20.43	7.447%	$21.9514	$21.95	$21.95	$22.00
Purchase #4	$123.76	12.749%	$139.5382	$139.54	$139.55	$139.50
Purchase #5	$62.58	13.655%	$71.1253	$71.13	$71.15	$71.10
Purchase #6	$250.33	6.827%	$267.42	$267.42	$267.40	$267.40
Purchase #7	$51.93	4.517%	$54.2757	$54.28	$54.30	$54.30
7 purchase totals =	$770.57		$838.2935	$838.30	$838.35	$838.20