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	$239.54	6.498%	$255.1053	$255.11	$255.10	$255.10
Purchase #2	$18.26	3.520%	$18.9028	$18.90	$18.90	$18.90
Purchase #3	$14.82	11.580%	$16.5362	$16.54	$16.55	$16.50
Purchase #4	$93.27	7.829%	$100.5721	$100.57	$100.55	$100.60
Purchase #5	$39.91	9.752%	$43.802	$43.80	$43.80	$43.80
Purchase #6	$18.53	8.453%	$20.0963	$20.10	$20.10	$20.10
Purchase #7	$218.75	11.609%	$244.1447	$244.14	$244.15	$244.10
7 purchase totals =	$643.08		$699.1594	$699.16	$699.15	$699.10