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	$206.98	12.839%	$233.5542	$233.55	$233.55	$233.60
Purchase #2	$61.71	7.361%	$66.2525	$66.25	$66.25	$66.30
Purchase #3	$126.95	13.268%	$143.7937	$143.79	$143.80	$143.80
Purchase #4	$141.73	4.847%	$148.5997	$148.60	$148.60	$148.60
Purchase #5	$37.99	11.478%	$42.3505	$42.35	$42.35	$42.40
Purchase #6	$123.85	4.266%	$129.1334	$129.13	$129.15	$129.10
Purchase #7	$223.33	7.188%	$239.383	$239.38	$239.40	$239.40
7 purchase totals =	$922.54		$1,003.0670	$1,003.05	$1,003.10	$1,003.20