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	$82.48	6.675%	$87.9855	$87.99	$88.00	$88.00
Purchase #2	$90.56	5.687%	$95.7101	$95.71	$95.70	$95.70
Purchase #3	$108.90	13.414%	$123.5078	$123.51	$123.50	$123.50
Purchase #4	$215.49	8.457%	$233.714	$233.71	$233.70	$233.70
Purchase #5	$179.71	4.683%	$188.1258	$188.13	$188.15	$188.10
Purchase #6	$67.48	5.496%	$71.1887	$71.19	$71.20	$71.20
Purchase #7	$123.38	11.171%	$137.1628	$137.16	$137.15	$137.20
7 purchase totals =	$868.00		$937.3947	$937.40	$937.40	$937.40