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	$31.87	4.598%	$33.3354	$33.34	$33.35	$33.30
Purchase #2	$56.62	6.138%	$60.0953	$60.10	$60.10	$60.10
Purchase #3	$36.96	11.707%	$41.2869	$41.29	$41.30	$41.30
Purchase #4	$37.74	12.534%	$42.4703	$42.47	$42.45	$42.50
Purchase #5	$132.48	12.308%	$148.7856	$148.79	$148.80	$148.80
Purchase #6	$141.28	12.394%	$158.7902	$158.79	$158.80	$158.80
Purchase #7	$172.98	3.342%	$178.761	$178.76	$178.75	$178.80
7 purchase totals =	$609.93		$663.5247	$663.54	$663.55	$663.60