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	$17.76	11.506%	$19.8035	$19.80	$19.80	$19.80
Purchase #2	$119.74	12.678%	$134.9206	$134.92	$134.90	$134.90
Purchase #3	$10.92	5.712%	$11.5438	$11.54	$11.55	$11.50
Purchase #4	$50.29	12.384%	$56.5179	$56.52	$56.50	$56.50
Purchase #5	$106.94	11.540%	$119.2809	$119.28	$119.30	$119.30
Purchase #6	$124.41	3.300%	$128.5155	$128.52	$128.50	$128.50
Purchase #7	$183.25	3.565%	$189.7829	$189.78	$189.80	$189.80
7 purchase totals =	$613.31		$660.3651	$660.36	$660.35	$660.30