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	$97.87	7.738%	$105.4432	$105.44	$105.45	$105.40
Purchase #2	$38.81	11.133%	$43.1307	$43.13	$43.15	$43.10
Purchase #3	$247.76	12.679%	$279.1735	$279.17	$279.15	$279.20
Purchase #4	$77.86	9.387%	$85.1687	$85.17	$85.15	$85.20
Purchase #5	$231.77	6.374%	$246.543	$246.54	$246.55	$246.50
Purchase #6	$61.36	5.632%	$64.8158	$64.82	$64.80	$64.80
Purchase #7	$103.43	10.376%	$114.1619	$114.16	$114.15	$114.20
7 purchase totals =	$858.86		$938.4368	$938.43	$938.40	$938.40