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	$90.54	13.819%	$103.0517	$103.05	$103.05	$103.10
Purchase #2	$108.69	13.521%	$123.386	$123.39	$123.40	$123.40
Purchase #3	$63.87	10.108%	$70.326	$70.33	$70.35	$70.30
Purchase #4	$53.56	3.140%	$55.2418	$55.24	$55.25	$55.20
Purchase #5	$69.93	8.867%	$76.1307	$76.13	$76.15	$76.10
Purchase #6	$49.78	13.114%	$56.3081	$56.31	$56.30	$56.30
Purchase #7	$21.76	11.118%	$24.1793	$24.18	$24.20	$24.20
7 purchase totals =	$458.13		$508.6236	$508.63	$508.70	$508.60