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	$30.85	4.321%	$32.183	$32.18	$32.20	$32.20
Purchase #2	$214.31	13.184%	$242.5646	$242.56	$242.55	$242.60
Purchase #3	$171.40	11.835%	$191.6852	$191.69	$191.70	$191.70
Purchase #4	$29.28	13.183%	$33.14	$33.14	$33.15	$33.10
Purchase #5	$31.67	8.616%	$34.3987	$34.40	$34.40	$34.40
Purchase #6	$89.40	11.507%	$99.6873	$99.69	$99.70	$99.70
Purchase #7	$157.60	9.704%	$172.8935	$172.89	$172.90	$172.90
7 purchase totals =	$724.51		$806.5523	$806.55	$806.60	$806.60