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	$166.62	13.324%	$188.8204	$188.82	$188.80	$188.80
Purchase #2	$124.72	10.722%	$138.0925	$138.09	$138.10	$138.10
Purchase #3	$192.35	9.719%	$211.0445	$211.04	$211.05	$211.00
Purchase #4	$119.76	6.179%	$127.16	$127.16	$127.15	$127.20
Purchase #5	$204.57	8.612%	$222.1876	$222.19	$222.20	$222.20
Purchase #6	$179.42	3.759%	$186.1644	$186.16	$186.15	$186.20
Purchase #7	$33.31	13.402%	$37.7742	$37.77	$37.75	$37.80
7 purchase totals =	$1,020.75		$1,111.2436	$1,111.23	$1,111.20	$1,111.30