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	$42.62	6.811%	$45.5228	$45.52	$45.50	$45.50
Purchase #2	$61.93	3.387%	$64.0276	$64.03	$64.05	$64.00
Purchase #3	$190.51	6.371%	$202.6474	$202.65	$202.65	$202.60
Purchase #4	$235.79	13.349%	$267.2656	$267.27	$267.25	$267.30
Purchase #5	$98.39	4.737%	$103.0507	$103.05	$103.05	$103.10
Purchase #6	$150.77	11.805%	$168.5684	$168.57	$168.55	$168.60
Purchase #7	$137.88	3.329%	$142.47	$142.47	$142.45	$142.50
7 purchase totals =	$917.89		$993.5525	$993.56	$993.50	$993.60