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	$129.75	13.398%	$147.1339	$147.13	$147.15	$147.10
Purchase #2	$90.79	8.333%	$98.3555	$98.36	$98.35	$98.40
Purchase #3	$232.37	9.409%	$254.2337	$254.23	$254.25	$254.20
Purchase #4	$11.80	8.702%	$12.8268	$12.83	$12.85	$12.80
Purchase #5	$235.84	8.160%	$255.0845	$255.08	$255.10	$255.10
Purchase #6	$98.36	11.330%	$109.5042	$109.50	$109.50	$109.50
Purchase #7	$169.92	6.155%	$180.3786	$180.38	$180.40	$180.40
7 purchase totals =	$968.83		$1,057.5172	$1,057.51	$1,057.60	$1,057.50