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	$15.91	4.345%	$16.6013	$16.60	$16.60	$16.60
Purchase #2	$57.41	4.239%	$59.8436	$59.84	$59.85	$59.80
Purchase #3	$33.75	12.642%	$38.0167	$38.02	$38.00	$38.00
Purchase #4	$181.51	4.273%	$189.2659	$189.27	$189.25	$189.30
Purchase #5	$205.36	6.583%	$218.8788	$218.88	$218.90	$218.90
Purchase #6	$29.62	6.318%	$31.4914	$31.49	$31.50	$31.50
Purchase #7	$134.26	13.402%	$152.2535	$152.25	$152.25	$152.30
7 purchase totals =	$657.82		$706.3512	$706.35	$706.35	$706.40