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	$110.43	7.327%	$118.5212	$118.52	$118.50	$118.50
Purchase #2	$38.77	11.456%	$43.2115	$43.21	$43.20	$43.20
Purchase #3	$209.25	6.251%	$222.3302	$222.33	$222.35	$222.30
Purchase #4	$144.72	7.619%	$155.7462	$155.75	$155.75	$155.70
Purchase #5	$189.32	3.581%	$196.0995	$196.10	$196.10	$196.10
Purchase #6	$226.32	9.480%	$247.7751	$247.78	$247.80	$247.80
Purchase #7	$134.38	3.624%	$139.2499	$139.25	$139.25	$139.20
7 purchase totals =	$1,053.19		$1,122.9336	$1,122.94	$1,122.95	$1,122.80