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	$68.46	3.747%	$71.0252	$71.03	$71.05	$71.00
Purchase #2	$214.75	12.374%	$241.3232	$241.32	$241.30	$241.30
Purchase #3	$146.96	9.524%	$160.9565	$160.96	$160.95	$161.00
Purchase #4	$54.25	12.152%	$60.8425	$60.84	$60.85	$60.80
Purchase #5	$13.73	12.524%	$15.4495	$15.45	$15.45	$15.40
Purchase #6	$33.30	6.116%	$35.3366	$35.34	$35.35	$35.30
Purchase #7	$79.33	12.701%	$89.4057	$89.41	$89.40	$89.40
7 purchase totals =	$610.78		$674.3392	$674.35	$674.35	$674.20