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	$162.85	12.649%	$183.4489	$183.45	$183.45	$183.40
Purchase #2	$36.42	13.161%	$41.2132	$41.21	$41.20	$41.20
Purchase #3	$218.52	11.307%	$243.2281	$243.23	$243.25	$243.20
Purchase #4	$74.92	9.859%	$82.3064	$82.31	$82.30	$82.30
Purchase #5	$177.37	4.370%	$185.1211	$185.12	$185.10	$185.10
Purchase #6	$169.30	3.562%	$175.3305	$175.33	$175.35	$175.30
Purchase #7	$40.82	6.350%	$43.4121	$43.41	$43.40	$43.40
7 purchase totals =	$880.20		$954.0603	$954.06	$954.05	$953.90