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	$30.93	9.309%	$33.8093	$33.81	$33.80	$33.80
Purchase #2	$159.80	7.616%	$171.9704	$171.97	$171.95	$172.00
Purchase #3	$94.50	3.843%	$98.1316	$98.13	$98.15	$98.10
Purchase #4	$200.41	3.629%	$207.6829	$207.68	$207.70	$207.70
Purchase #5	$152.54	13.285%	$172.8049	$172.80	$172.80	$172.80
Purchase #6	$95.56	5.265%	$100.5912	$100.59	$100.60	$100.60
Purchase #7	$66.78	8.718%	$72.6019	$72.60	$72.60	$72.60
7 purchase totals =	$800.52		$857.5922	$857.58	$857.60	$857.60