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	$54.98	6.597%	$58.607	$58.61	$58.60	$58.60
Purchase #2	$150.28	8.268%	$162.7052	$162.71	$162.70	$162.70
Purchase #3	$100.51	8.771%	$109.3257	$109.33	$109.35	$109.30
Purchase #4	$18.47	9.224%	$20.1737	$20.17	$20.15	$20.20
Purchase #5	$242.58	9.557%	$265.7634	$265.76	$265.75	$265.80
Purchase #6	$31.41	3.231%	$32.4249	$32.42	$32.40	$32.40
Purchase #7	$158.55	13.538%	$180.0145	$180.01	$180.00	$180.00
7 purchase totals =	$756.78		$829.0144	$829.01	$828.95	$829.00