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	$72.56	3.499%	$75.0989	$75.10	$75.10	$75.10
Purchase #2	$57.32	7.258%	$61.4803	$61.48	$61.50	$61.50
Purchase #3	$103.89	7.172%	$111.341	$111.34	$111.35	$111.30
Purchase #4	$144.42	7.342%	$155.0233	$155.02	$155.00	$155.00
Purchase #5	$113.32	6.161%	$120.3016	$120.30	$120.30	$120.30
Purchase #6	$69.85	9.234%	$76.2999	$76.30	$76.30	$76.30
Purchase #7	$65.75	9.491%	$71.9903	$71.99	$72.00	$72.00
7 purchase totals =	$627.11		$671.5353	$671.53	$671.55	$671.50