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	$177.83	6.701%	$189.7464	$189.75	$189.75	$189.70
Purchase #2	$128.58	7.753%	$138.5488	$138.55	$138.55	$138.50
Purchase #3	$92.41	12.304%	$103.7801	$103.78	$103.80	$103.80
Purchase #4	$85.64	8.421%	$92.8517	$92.85	$92.85	$92.90
Purchase #5	$214.37	11.374%	$238.7524	$238.75	$238.75	$238.80
Purchase #6	$34.28	10.584%	$37.9082	$37.91	$37.90	$37.90
Purchase #7	$161.70	6.558%	$172.3043	$172.30	$172.30	$172.30
7 purchase totals =	$894.81		$973.8919	$973.89	$973.90	$973.90