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	$206.85	7.523%	$222.4113	$222.41	$222.40	$222.40
Purchase #2	$73.88	6.548%	$78.7177	$78.72	$78.70	$78.70
Purchase #3	$182.73	9.349%	$199.8134	$199.81	$199.80	$199.80
Purchase #4	$33.85	7.431%	$36.3654	$36.37	$36.35	$36.40
Purchase #5	$133.43	4.463%	$139.385	$139.39	$139.40	$139.40
Purchase #6	$132.27	8.602%	$143.6479	$143.65	$143.65	$143.60
Purchase #7	$85.37	6.835%	$91.205	$91.21	$91.20	$91.20
7 purchase totals =	$848.38		$911.5457	$911.56	$911.50	$911.50