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	$101.31	10.732%	$112.1826	$112.18	$112.20	$112.20
Purchase #2	$200.69	6.326%	$213.3856	$213.39	$213.40	$213.40
Purchase #3	$57.99	11.199%	$64.4843	$64.48	$64.50	$64.50
Purchase #4	$169.82	11.583%	$189.4903	$189.49	$189.50	$189.50
Purchase #5	$92.82	9.613%	$101.7428	$101.74	$101.75	$101.70
Purchase #6	$50.52	12.172%	$56.6693	$56.67	$56.65	$56.70
Purchase #7	$95.25	11.828%	$106.5162	$106.52	$106.50	$106.50
7 purchase totals =	$768.40		$844.4711	$844.47	$844.50	$844.50