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	$232.45	13.435%	$263.6797	$263.68	$263.70	$263.70
Purchase #2	$26.46	9.217%	$28.8988	$28.90	$28.90	$28.90
Purchase #3	$25.76	8.221%	$27.8777	$27.88	$27.90	$27.90
Purchase #4	$31.89	13.106%	$36.0695	$36.07	$36.05	$36.10
Purchase #5	$37.76	8.615%	$41.013	$41.01	$41.00	$41.00
Purchase #6	$140.98	5.612%	$148.8918	$148.89	$148.90	$148.90
Purchase #7	$105.96	12.149%	$118.8331	$118.83	$118.85	$118.80
7 purchase totals =	$601.26		$665.2636	$665.26	$665.30	$665.30