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	$57.27	9.150%	$62.5102	$62.51	$62.50	$62.50
Purchase #2	$100.54	10.511%	$111.1078	$111.11	$111.10	$111.10
Purchase #3	$19.44	4.145%	$20.2458	$20.25	$20.25	$20.20
Purchase #4	$93.46	4.817%	$97.962	$97.96	$97.95	$98.00
Purchase #5	$88.68	11.467%	$98.8489	$98.85	$98.85	$98.80
Purchase #6	$129.91	7.326%	$139.4272	$139.43	$139.45	$139.40
Purchase #7	$247.25	8.343%	$267.8781	$267.88	$267.90	$267.90
7 purchase totals =	$736.55		$797.9800	$797.99	$798.00	$797.90