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	$249.86	3.851%	$259.4821	$259.48	$259.50	$259.50
Purchase #2	$41.47	12.119%	$46.4957	$46.50	$46.50	$46.50
Purchase #3	$50.82	12.449%	$57.1466	$57.15	$57.15	$57.10
Purchase #4	$223.77	10.820%	$247.9819	$247.98	$248.00	$248.00
Purchase #5	$157.71	7.399%	$169.379	$169.38	$169.40	$169.40
Purchase #6	$54.32	3.397%	$56.1653	$56.17	$56.15	$56.20
Purchase #7	$29.92	8.258%	$32.3908	$32.39	$32.40	$32.40
7 purchase totals =	$807.87		$869.0414	$869.05	$869.10	$869.10