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	$134.52	9.302%	$147.0331	$147.03	$147.05	$147.00
Purchase #2	$45.47	11.771%	$50.8223	$50.82	$50.80	$50.80
Purchase #3	$19.53	4.759%	$20.4594	$20.46	$20.45	$20.50
Purchase #4	$103.88	5.680%	$109.7804	$109.78	$109.80	$109.80
Purchase #5	$212.25	7.467%	$228.0987	$228.10	$228.10	$228.10
Purchase #6	$162.80	11.189%	$181.0157	$181.02	$181.00	$181.00
Purchase #7	$57.45	10.507%	$63.4863	$63.49	$63.50	$63.50
7 purchase totals =	$735.90		$800.6959	$800.70	$800.70	$800.70