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	$78.29	13.665%	$88.9883	$88.99	$89.00	$89.00
Purchase #2	$80.61	11.501%	$89.881	$89.88	$89.90	$89.90
Purchase #3	$173.55	11.834%	$194.0879	$194.09	$194.10	$194.10
Purchase #4	$161.99	11.737%	$181.0028	$181.00	$181.00	$181.00
Purchase #5	$7.98	10.542%	$8.8213	$8.82	$8.80	$8.80
Purchase #6	$241.49	8.150%	$261.1714	$261.17	$261.15	$261.20
Purchase #7	$57.87	3.573%	$59.9377	$59.94	$59.95	$59.90
7 purchase totals =	$801.78		$883.8904	$883.89	$883.90	$883.90