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	$143.63	11.761%	$160.5223	$160.52	$160.50	$160.50
Purchase #2	$141.64	6.123%	$150.3126	$150.31	$150.30	$150.30
Purchase #3	$126.26	4.489%	$131.9278	$131.93	$131.95	$131.90
Purchase #4	$140.37	8.518%	$152.3267	$152.33	$152.35	$152.30
Purchase #5	$59.42	8.640%	$64.5539	$64.55	$64.55	$64.60
Purchase #6	$128.26	13.590%	$145.6905	$145.69	$145.70	$145.70
Purchase #7	$74.29	12.835%	$83.8251	$83.83	$83.85	$83.80
7 purchase totals =	$813.87		$889.1589	$889.16	$889.20	$889.10