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	$204.51	3.669%	$212.0135	$212.01	$212.00	$212.00
Purchase #2	$87.79	3.273%	$90.6634	$90.66	$90.65	$90.70
Purchase #3	$46.26	5.612%	$48.8561	$48.86	$48.85	$48.90
Purchase #4	$235.85	5.759%	$249.4326	$249.43	$249.45	$249.40
Purchase #5	$73.92	11.305%	$82.2767	$82.28	$82.30	$82.30
Purchase #6	$183.38	7.108%	$196.4147	$196.41	$196.40	$196.40
Purchase #7	$104.83	13.559%	$119.0439	$119.04	$119.05	$119.00
7 purchase totals =	$936.54		$998.7009	$998.69	$998.70	$998.70