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	$190.58	3.213%	$196.7033	$196.70	$196.70	$196.70
Purchase #2	$67.26	11.537%	$75.0198	$75.02	$75.00	$75.00
Purchase #3	$66.25	9.249%	$72.3775	$72.38	$72.40	$72.40
Purchase #4	$133.39	3.105%	$137.5318	$137.53	$137.55	$137.50
Purchase #5	$144.33	4.333%	$150.5838	$150.58	$150.60	$150.60
Purchase #6	$67.96	4.510%	$71.025	$71.03	$71.05	$71.00
Purchase #7	$115.66	9.609%	$126.7738	$126.77	$126.75	$126.80
7 purchase totals =	$785.43		$830.0150	$830.01	$830.05	$830.00