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	$19.90	4.598%	$20.815	$20.82	$20.80	$20.80
Purchase #2	$30.32	6.487%	$32.2869	$32.29	$32.30	$32.30
Purchase #3	$210.97	7.666%	$227.143	$227.14	$227.15	$227.10
Purchase #4	$27.63	5.357%	$29.1101	$29.11	$29.10	$29.10
Purchase #5	$119.38	4.145%	$124.3283	$124.33	$124.35	$124.30
Purchase #6	$208.54	7.649%	$224.4912	$224.49	$224.50	$224.50
Purchase #7	$82.79	13.667%	$94.1049	$94.10	$94.10	$94.10
7 purchase totals =	$699.53		$752.2794	$752.28	$752.30	$752.20