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	$160.59	3.311%	$165.9071	$165.91	$165.90	$165.90
Purchase #2	$28.49	3.766%	$29.5629	$29.56	$29.55	$29.60
Purchase #3	$131.59	8.558%	$142.8515	$142.85	$142.85	$142.90
Purchase #4	$94.92	8.402%	$102.8952	$102.90	$102.90	$102.90
Purchase #5	$194.93	7.174%	$208.9143	$208.91	$208.90	$208.90
Purchase #6	$29.48	9.341%	$32.2337	$32.23	$32.25	$32.20
Purchase #7	$139.66	5.129%	$146.8232	$146.82	$146.80	$146.80
7 purchase totals =	$779.66		$829.1879	$829.18	$829.15	$829.20