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	$91.99	8.154%	$99.4909	$99.49	$99.50	$99.50
Purchase #2	$151.50	3.182%	$156.3207	$156.32	$156.30	$156.30
Purchase #3	$132.62	9.665%	$145.4377	$145.44	$145.45	$145.40
Purchase #4	$157.57	6.597%	$167.9649	$167.96	$167.95	$168.00
Purchase #5	$134.90	4.472%	$140.9327	$140.93	$140.95	$140.90
Purchase #6	$145.54	11.134%	$161.7444	$161.74	$161.75	$161.70
Purchase #7	$222.26	4.222%	$231.6438	$231.64	$231.65	$231.60
7 purchase totals =	$1,036.38		$1,103.5351	$1,103.52	$1,103.55	$1,103.40