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	$5.63	12.311%	$6.3231	$6.32	$6.30	$6.30
Purchase #2	$198.88	9.872%	$218.5134	$218.51	$218.50	$218.50
Purchase #3	$165.45	3.607%	$171.4178	$171.42	$171.40	$171.40
Purchase #4	$9.33	9.733%	$10.2381	$10.24	$10.25	$10.20
Purchase #5	$18.99	10.130%	$20.9137	$20.91	$20.90	$20.90
Purchase #6	$215.31	4.622%	$225.2616	$225.26	$225.25	$225.30
Purchase #7	$47.33	9.572%	$51.8604	$51.86	$51.85	$51.90
7 purchase totals =	$660.92		$704.5281	$704.52	$704.45	$704.50