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	$67.40	7.134%	$72.2083	$72.21	$72.20	$72.20
Purchase #2	$233.25	10.415%	$257.543	$257.54	$257.55	$257.50
Purchase #3	$81.63	8.375%	$88.4665	$88.47	$88.45	$88.50
Purchase #4	$91.74	10.623%	$101.4855	$101.49	$101.50	$101.50
Purchase #5	$107.50	4.761%	$112.6181	$112.62	$112.60	$112.60
Purchase #6	$100.62	11.595%	$112.2869	$112.29	$112.30	$112.30
Purchase #7	$31.38	4.184%	$32.6929	$32.69	$32.70	$32.70
7 purchase totals =	$713.52		$777.3012	$777.31	$777.30	$777.30