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	$18.80	3.147%	$19.3916	$19.39	$19.40	$19.40
Purchase #2	$50.30	6.476%	$53.5574	$53.56	$53.55	$53.60
Purchase #3	$133.94	8.466%	$145.2794	$145.28	$145.30	$145.30
Purchase #4	$175.41	6.620%	$187.0221	$187.02	$187.00	$187.00
Purchase #5	$154.54	11.206%	$171.8578	$171.86	$171.85	$171.90
Purchase #6	$109.50	8.285%	$118.5721	$118.57	$118.55	$118.60
Purchase #7	$28.53	13.531%	$32.3904	$32.39	$32.40	$32.40
7 purchase totals =	$671.02		$728.0708	$728.07	$728.05	$728.20