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	$247.71	10.727%	$274.2819	$274.28	$274.30	$274.30
Purchase #2	$177.93	4.434%	$185.8194	$185.82	$185.80	$185.80
Purchase #3	$74.70	11.181%	$83.0522	$83.05	$83.05	$83.10
Purchase #4	$133.39	7.604%	$143.533	$143.53	$143.55	$143.50
Purchase #5	$35.47	5.430%	$37.396	$37.40	$37.40	$37.40
Purchase #6	$27.93	12.463%	$31.4109	$31.41	$31.40	$31.40
Purchase #7	$43.91	10.145%	$48.3647	$48.36	$48.35	$48.40
7 purchase totals =	$741.04		$803.8581	$803.85	$803.85	$803.90