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	$246.90	11.450%	$275.1701	$275.17	$275.15	$275.20
Purchase #2	$125.64	8.591%	$136.4337	$136.43	$136.45	$136.40
Purchase #3	$77.76	11.483%	$86.6892	$86.69	$86.70	$86.70
Purchase #4	$62.42	7.427%	$67.0559	$67.06	$67.05	$67.10
Purchase #5	$76.52	11.538%	$85.3489	$85.35	$85.35	$85.30
Purchase #6	$80.65	3.376%	$83.3727	$83.37	$83.35	$83.40
Purchase #7	$249.62	3.273%	$257.7901	$257.79	$257.80	$257.80
7 purchase totals =	$919.51		$991.8606	$991.86	$991.85	$991.90