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	$137.28	8.414%	$148.8307	$148.83	$148.85	$148.80
Purchase #2	$67.70	3.300%	$69.9341	$69.93	$69.95	$69.90
Purchase #3	$99.42	12.817%	$112.1627	$112.16	$112.15	$112.20
Purchase #4	$171.31	4.755%	$179.4558	$179.46	$179.45	$179.50
Purchase #5	$249.44	12.797%	$281.3608	$281.36	$281.35	$281.40
Purchase #6	$111.65	9.772%	$122.5604	$122.56	$122.55	$122.60
Purchase #7	$177.76	4.537%	$185.825	$185.83	$185.85	$185.80
7 purchase totals =	$1,014.56		$1,100.1295	$1,100.13	$1,100.15	$1,100.20