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	$112.35	6.727%	$119.9078	$119.91	$119.90	$119.90
Purchase #2	$225.98	7.793%	$243.5906	$243.59	$243.60	$243.60
Purchase #3	$127.34	9.830%	$139.8575	$139.86	$139.85	$139.90
Purchase #4	$15.28	11.729%	$17.0722	$17.07	$17.05	$17.10
Purchase #5	$149.44	10.615%	$165.3031	$165.30	$165.30	$165.30
Purchase #6	$59.50	11.770%	$66.5032	$66.50	$66.50	$66.50
Purchase #7	$16.93	7.732%	$18.239	$18.24	$18.25	$18.20
7 purchase totals =	$706.82		$770.4734	$770.47	$770.45	$770.50