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	$28.75	12.255%	$32.2733	$32.27	$32.25	$32.30
Purchase #2	$38.36	9.846%	$42.1369	$42.14	$42.15	$42.10
Purchase #3	$27.76	13.801%	$31.5912	$31.59	$31.60	$31.60
Purchase #4	$37.54	12.304%	$42.1589	$42.16	$42.15	$42.20
Purchase #5	$5.69	12.327%	$6.3914	$6.39	$6.40	$6.40
Purchase #6	$163.63	5.413%	$172.4873	$172.49	$172.50	$172.50
Purchase #7	$16.99	3.193%	$17.5325	$17.53	$17.55	$17.50
7 purchase totals =	$318.72		$344.5715	$344.57	$344.60	$344.60