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	$141.95	11.317%	$158.0145	$158.01	$158.00	$158.00
Purchase #2	$65.94	12.687%	$74.3058	$74.31	$74.30	$74.30
Purchase #3	$212.48	13.723%	$241.6386	$241.64	$241.65	$241.60
Purchase #4	$71.98	8.579%	$78.1552	$78.16	$78.15	$78.20
Purchase #5	$201.38	13.182%	$227.9259	$227.93	$227.95	$227.90
Purchase #6	$179.72	5.104%	$188.8929	$188.89	$188.90	$188.90
Purchase #7	$204.27	9.125%	$222.9096	$222.91	$222.90	$222.90
7 purchase totals =	$1,077.72		$1,191.8425	$1,191.85	$1,191.85	$1,191.80