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	$144.74	5.796%	$153.1291	$153.13	$153.15	$153.10
Purchase #2	$136.88	7.121%	$146.6272	$146.63	$146.65	$146.60
Purchase #3	$130.40	7.181%	$139.764	$139.76	$139.75	$139.80
Purchase #4	$175.52	3.211%	$181.1559	$181.16	$181.15	$181.20
Purchase #5	$201.96	10.824%	$223.8202	$223.82	$223.80	$223.80
Purchase #6	$132.87	3.497%	$137.5165	$137.52	$137.50	$137.50
Purchase #7	$101.87	5.481%	$107.4535	$107.45	$107.45	$107.50
7 purchase totals =	$1,024.24		$1,089.4664	$1,089.47	$1,089.45	$1,089.50