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	$113.60	13.537%	$128.978	$128.98	$129.00	$129.00
Purchase #2	$96.41	9.846%	$105.9025	$105.90	$105.90	$105.90
Purchase #3	$19.61	12.751%	$22.1105	$22.11	$22.10	$22.10
Purchase #4	$128.37	3.211%	$132.492	$132.49	$132.50	$132.50
Purchase #5	$36.71	11.383%	$40.8887	$40.89	$40.90	$40.90
Purchase #6	$32.84	11.701%	$36.6826	$36.68	$36.70	$36.70
Purchase #7	$6.61	10.377%	$7.2959	$7.30	$7.30	$7.30
7 purchase totals =	$434.15		$474.3502	$474.35	$474.40	$474.40