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	$5.77	4.402%	$6.024	$6.02	$6.00	$6.00
Purchase #2	$129.40	10.778%	$143.3467	$143.35	$143.35	$143.30
Purchase #3	$110.33	12.357%	$123.9635	$123.96	$123.95	$124.00
Purchase #4	$41.75	13.262%	$47.2869	$47.29	$47.30	$47.30
Purchase #5	$206.76	7.449%	$222.1616	$222.16	$222.15	$222.20
Purchase #6	$151.28	3.791%	$157.015	$157.02	$157.00	$157.00
Purchase #7	$40.53	6.846%	$43.3047	$43.30	$43.30	$43.30
7 purchase totals =	$685.82		$743.1024	$743.10	$743.05	$743.10