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	$192.34	11.869%	$215.1688	$215.17	$215.15	$215.20
Purchase #2	$143.92	13.153%	$162.8498	$162.85	$162.85	$162.80
Purchase #3	$224.83	8.231%	$243.3358	$243.34	$243.35	$243.30
Purchase #4	$30.94	7.394%	$33.2277	$33.23	$33.25	$33.20
Purchase #5	$144.44	3.850%	$150.0009	$150.00	$150.00	$150.00
Purchase #6	$40.31	12.737%	$45.4443	$45.44	$45.45	$45.40
Purchase #7	$47.66	5.650%	$50.3528	$50.35	$50.35	$50.40
7 purchase totals =	$824.44		$900.3801	$900.38	$900.40	$900.30