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	$37.97	5.762%	$40.1578	$40.16	$40.15	$40.20
Purchase #2	$65.61	10.507%	$72.5036	$72.50	$72.50	$72.50
Purchase #3	$154.87	9.431%	$169.4758	$169.48	$169.50	$169.50
Purchase #4	$124.28	5.609%	$131.2509	$131.25	$131.25	$131.30
Purchase #5	$222.26	11.447%	$247.7021	$247.70	$247.70	$247.70
Purchase #6	$14.90	4.604%	$15.586	$15.59	$15.60	$15.60
Purchase #7	$194.49	6.157%	$206.4647	$206.46	$206.45	$206.50
7 purchase totals =	$814.38		$883.1409	$883.14	$883.15	$883.30