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	$239.31	5.141%	$251.6129	$251.61	$251.60	$251.60
Purchase #2	$216.53	8.290%	$234.4803	$234.48	$234.50	$234.50
Purchase #3	$205.30	9.360%	$224.5161	$224.52	$224.50	$224.50
Purchase #4	$146.75	6.234%	$155.8984	$155.90	$155.90	$155.90
Purchase #5	$72.69	11.152%	$80.7964	$80.80	$80.80	$80.80
Purchase #6	$99.25	13.720%	$112.8671	$112.87	$112.85	$112.90
Purchase #7	$202.28	6.374%	$215.1733	$215.17	$215.15	$215.20
7 purchase totals =	$1,182.11		$1,275.3445	$1,275.35	$1,275.30	$1,275.40