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	$215.69	12.327%	$242.2781	$242.28	$242.30	$242.30
Purchase #2	$42.91	10.714%	$47.5074	$47.51	$47.50	$47.50
Purchase #3	$37.87	8.110%	$40.9413	$40.94	$40.95	$40.90
Purchase #4	$132.35	11.442%	$147.4935	$147.49	$147.50	$147.50
Purchase #5	$64.74	5.788%	$68.4872	$68.49	$68.50	$68.50
Purchase #6	$98.48	13.627%	$111.8999	$111.90	$111.90	$111.90
Purchase #7	$159.79	10.550%	$176.6478	$176.65	$176.65	$176.60
7 purchase totals =	$751.83		$835.2552	$835.26	$835.30	$835.20