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	$29.47	10.743%	$32.636	$32.64	$32.65	$32.60
Purchase #2	$240.29	3.722%	$249.2336	$249.23	$249.25	$249.20
Purchase #3	$6.25	3.245%	$6.4528	$6.45	$6.45	$6.50
Purchase #4	$242.42	10.680%	$268.3105	$268.31	$268.30	$268.30
Purchase #5	$120.57	13.772%	$137.1749	$137.17	$137.15	$137.20
Purchase #6	$95.34	4.146%	$99.2928	$99.29	$99.30	$99.30
Purchase #7	$225.80	7.786%	$243.3808	$243.38	$243.40	$243.40
7 purchase totals =	$960.14		$1,036.4814	$1,036.47	$1,036.50	$1,036.50