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	$53.52	7.503%	$57.5356	$57.54	$57.55	$57.50
Purchase #2	$111.57	8.371%	$120.9095	$120.91	$120.90	$120.90
Purchase #3	$215.82	8.180%	$233.4741	$233.47	$233.45	$233.50
Purchase #4	$214.63	4.654%	$224.6189	$224.62	$224.60	$224.60
Purchase #5	$13.75	10.411%	$15.1815	$15.18	$15.20	$15.20
Purchase #6	$91.40	4.309%	$95.3384	$95.34	$95.35	$95.30
Purchase #7	$42.37	7.131%	$45.3914	$45.39	$45.40	$45.40
7 purchase totals =	$743.06		$792.4494	$792.45	$792.45	$792.40