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	$202.55	3.585%	$209.8114	$209.81	$209.80	$209.80
Purchase #2	$108.52	13.588%	$123.2657	$123.27	$123.25	$123.30
Purchase #3	$78.26	6.683%	$83.4901	$83.49	$83.50	$83.50
Purchase #4	$81.65	11.795%	$91.2806	$91.28	$91.30	$91.30
Purchase #5	$52.53	9.199%	$57.3622	$57.36	$57.35	$57.40
Purchase #6	$30.50	6.491%	$32.4798	$32.48	$32.50	$32.50
Purchase #7	$57.46	7.764%	$61.9212	$61.92	$61.90	$61.90
7 purchase totals =	$611.47		$659.6110	$659.61	$659.60	$659.70