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	$29.71	8.710%	$32.2977	$32.30	$32.30	$32.30
Purchase #2	$181.77	3.727%	$188.5446	$188.54	$188.55	$188.50
Purchase #3	$40.49	12.246%	$45.4484	$45.45	$45.45	$45.40
Purchase #4	$48.33	12.179%	$54.2161	$54.22	$54.20	$54.20
Purchase #5	$198.40	12.469%	$223.1385	$223.14	$223.15	$223.10
Purchase #6	$227.93	4.184%	$237.4666	$237.47	$237.45	$237.50
Purchase #7	$17.67	4.340%	$18.4369	$18.44	$18.45	$18.40
7 purchase totals =	$744.30		$799.5488	$799.56	$799.55	$799.40