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	$41.50	4.130%	$43.214	$43.21	$43.20	$43.20
Purchase #2	$220.94	4.655%	$231.2248	$231.22	$231.20	$231.20
Purchase #3	$89.87	7.400%	$96.5204	$96.52	$96.50	$96.50
Purchase #4	$55.75	5.377%	$58.7477	$58.75	$58.75	$58.70
Purchase #5	$250.72	9.603%	$274.7966	$274.80	$274.80	$274.80
Purchase #6	$108.60	5.791%	$114.889	$114.89	$114.90	$114.90
Purchase #7	$105.96	5.481%	$111.7677	$111.77	$111.75	$111.80
7 purchase totals =	$873.34		$931.1602	$931.16	$931.10	$931.10