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	$14.59	6.638%	$15.5585	$15.56	$15.55	$15.60
Purchase #2	$61.44	7.430%	$66.005	$66.01	$66.00	$66.00
Purchase #3	$30.28	3.647%	$31.3843	$31.38	$31.40	$31.40
Purchase #4	$147.82	12.814%	$166.7617	$166.76	$166.75	$166.80
Purchase #5	$191.48	12.697%	$215.7922	$215.79	$215.80	$215.80
Purchase #6	$48.95	3.844%	$50.8316	$50.83	$50.85	$50.80
Purchase #7	$79.38	8.233%	$85.9154	$85.92	$85.90	$85.90
7 purchase totals =	$573.94		$632.2487	$632.25	$632.25	$632.30