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	$129.82	12.740%	$146.3591	$146.36	$146.35	$146.40
Purchase #2	$56.37	11.358%	$62.7725	$62.77	$62.75	$62.80
Purchase #3	$242.74	7.522%	$260.9989	$261.00	$261.00	$261.00
Purchase #4	$78.72	8.565%	$85.4624	$85.46	$85.45	$85.50
Purchase #5	$175.82	8.149%	$190.1476	$190.15	$190.15	$190.10
Purchase #6	$104.83	9.504%	$114.793	$114.79	$114.80	$114.80
Purchase #7	$186.63	5.470%	$196.8387	$196.84	$196.85	$196.80
7 purchase totals =	$974.93		$1,057.3722	$1,057.37	$1,057.35	$1,057.40