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	$93.81	10.639%	$103.7904	$103.79	$103.80	$103.80
Purchase #2	$61.25	3.560%	$63.4305	$63.43	$63.45	$63.40
Purchase #3	$134.72	9.311%	$147.2638	$147.26	$147.25	$147.30
Purchase #4	$39.89	10.333%	$44.0118	$44.01	$44.00	$44.00
Purchase #5	$107.52	3.835%	$111.6434	$111.64	$111.65	$111.60
Purchase #6	$200.64	10.670%	$222.0483	$222.05	$222.05	$222.00
Purchase #7	$89.55	8.373%	$97.048	$97.05	$97.05	$97.00
7 purchase totals =	$727.38		$789.2362	$789.23	$789.25	$789.10