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	$74.39	11.613%	$83.0289	$83.03	$83.05	$83.00
Purchase #2	$217.92	9.625%	$238.8948	$238.89	$238.90	$238.90
Purchase #3	$191.97	7.682%	$206.7171	$206.72	$206.70	$206.70
Purchase #4	$124.54	13.155%	$140.9232	$140.92	$140.90	$140.90
Purchase #5	$130.94	5.574%	$138.2386	$138.24	$138.25	$138.20
Purchase #6	$137.38	7.339%	$147.4623	$147.46	$147.45	$147.50
Purchase #7	$150.34	11.767%	$168.0305	$168.03	$168.05	$168.00
7 purchase totals =	$1,027.48		$1,123.2954	$1,123.29	$1,123.30	$1,123.20