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	$42.48	9.651%	$46.5797	$46.58	$46.60	$46.60
Purchase #2	$137.52	4.634%	$143.8927	$143.89	$143.90	$143.90
Purchase #3	$49.41	3.681%	$51.2288	$51.23	$51.25	$51.20
Purchase #4	$113.78	8.125%	$123.0246	$123.02	$123.00	$123.00
Purchase #5	$144.78	5.249%	$152.3795	$152.38	$152.40	$152.40
Purchase #6	$119.84	8.221%	$129.692	$129.69	$129.70	$129.70
Purchase #7	$248.52	13.227%	$281.3917	$281.39	$281.40	$281.40
7 purchase totals =	$856.33		$928.1890	$928.18	$928.25	$928.20