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	$96.91	3.272%	$100.0809	$100.08	$100.10	$100.10
Purchase #2	$116.79	13.692%	$132.7809	$132.78	$132.80	$132.80
Purchase #3	$121.64	7.855%	$131.1948	$131.19	$131.20	$131.20
Purchase #4	$137.82	10.404%	$152.1588	$152.16	$152.15	$152.20
Purchase #5	$32.77	13.796%	$37.2909	$37.29	$37.30	$37.30
Purchase #6	$99.36	7.253%	$106.5666	$106.57	$106.55	$106.60
Purchase #7	$162.70	9.256%	$177.7595	$177.76	$177.75	$177.80
7 purchase totals =	$767.99		$837.8324	$837.83	$837.85	$838.00