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	$218.75	13.517%	$248.3184	$248.32	$248.30	$248.30
Purchase #2	$37.48	10.818%	$41.5346	$41.53	$41.55	$41.50
Purchase #3	$45.69	9.556%	$50.0561	$50.06	$50.05	$50.10
Purchase #4	$74.87	10.214%	$82.5172	$82.52	$82.50	$82.50
Purchase #5	$20.68	5.552%	$21.8282	$21.83	$21.85	$21.80
Purchase #6	$151.87	6.363%	$161.5335	$161.53	$161.55	$161.50
Purchase #7	$234.92	3.704%	$243.6214	$243.62	$243.60	$243.60
7 purchase totals =	$784.26		$849.4094	$849.41	$849.40	$849.30