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	$200.41	6.706%	$213.8495	$213.85	$213.85	$213.80
Purchase #2	$49.74	13.370%	$56.3902	$56.39	$56.40	$56.40
Purchase #3	$246.29	5.425%	$259.6512	$259.65	$259.65	$259.70
Purchase #4	$144.51	3.378%	$149.3915	$149.39	$149.40	$149.40
Purchase #5	$67.37	6.263%	$71.5894	$71.59	$71.60	$71.60
Purchase #6	$211.52	10.811%	$234.3874	$234.39	$234.40	$234.40
Purchase #7	$28.73	12.491%	$32.3187	$32.32	$32.30	$32.30
7 purchase totals =	$948.57		$1,017.5779	$1,017.58	$1,017.60	$1,017.60