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	$82.65	10.576%	$91.3911	$91.39	$91.40	$91.40
Purchase #2	$27.35	13.639%	$31.0803	$31.08	$31.10	$31.10
Purchase #3	$127.92	6.591%	$136.3512	$136.35	$136.35	$136.40
Purchase #4	$19.74	4.237%	$20.5764	$20.58	$20.60	$20.60
Purchase #5	$30.60	9.657%	$33.555	$33.56	$33.55	$33.60
Purchase #6	$218.71	9.757%	$240.0495	$240.05	$240.05	$240.00
Purchase #7	$172.47	7.268%	$185.0051	$185.01	$185.00	$185.00
7 purchase totals =	$679.44		$738.0086	$738.02	$738.05	$738.10