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	$129.86	4.854%	$136.1634	$136.16	$136.15	$136.20
Purchase #2	$82.28	11.261%	$91.5456	$91.55	$91.55	$91.50
Purchase #3	$191.33	11.646%	$213.6123	$213.61	$213.60	$213.60
Purchase #4	$235.26	5.492%	$248.1805	$248.18	$248.20	$248.20
Purchase #5	$34.49	11.850%	$38.5771	$38.58	$38.60	$38.60
Purchase #6	$72.82	13.352%	$82.5429	$82.54	$82.55	$82.50
Purchase #7	$149.86	6.429%	$159.4945	$159.49	$159.50	$159.50
7 purchase totals =	$895.90		$970.1163	$970.11	$970.15	$970.10