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	$16.59	11.234%	$18.4537	$18.45	$18.45	$18.50
Purchase #2	$155.34	6.333%	$165.1777	$165.18	$165.20	$165.20
Purchase #3	$37.66	12.788%	$42.476	$42.48	$42.50	$42.50
Purchase #4	$149.51	11.621%	$166.8846	$166.88	$166.90	$166.90
Purchase #5	$242.27	5.597%	$255.8299	$255.83	$255.85	$255.80
Purchase #6	$189.81	12.709%	$213.933	$213.93	$213.95	$213.90
Purchase #7	$204.41	9.413%	$223.6511	$223.65	$223.65	$223.70
7 purchase totals =	$995.59		$1,086.4060	$1,086.40	$1,086.50	$1,086.50