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	$237.30	5.850%	$251.1821	$251.18	$251.20	$251.20
Purchase #2	$37.68	12.366%	$42.3395	$42.34	$42.35	$42.30
Purchase #3	$202.57	3.559%	$209.7795	$209.78	$209.80	$209.80
Purchase #4	$183.81	9.423%	$201.1304	$201.13	$201.15	$201.10
Purchase #5	$54.84	11.636%	$61.2212	$61.22	$61.20	$61.20
Purchase #6	$78.91	13.256%	$89.3703	$89.37	$89.35	$89.40
Purchase #7	$41.43	10.276%	$45.6873	$45.69	$45.70	$45.70
7 purchase totals =	$836.54		$900.7103	$900.71	$900.75	$900.70