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	$241.88	3.620%	$250.6361	$250.64	$250.65	$250.60
Purchase #2	$74.80	9.804%	$82.1334	$82.13	$82.15	$82.10
Purchase #3	$150.35	3.795%	$156.0558	$156.06	$156.05	$156.10
Purchase #4	$101.70	7.403%	$109.2289	$109.23	$109.25	$109.20
Purchase #5	$142.79	11.589%	$159.3379	$159.34	$159.35	$159.30
Purchase #6	$39.48	3.403%	$40.8235	$40.82	$40.80	$40.80
Purchase #7	$136.33	13.389%	$154.5832	$154.58	$154.60	$154.60
7 purchase totals =	$887.33		$952.7988	$952.80	$952.85	$952.70