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	$79.73	11.743%	$89.0927	$89.09	$89.10	$89.10
Purchase #2	$133.57	13.334%	$151.3802	$151.38	$151.40	$151.40
Purchase #3	$102.28	11.855%	$114.4053	$114.41	$114.40	$114.40
Purchase #4	$140.92	10.705%	$156.0055	$156.01	$156.00	$156.00
Purchase #5	$65.89	5.393%	$69.4434	$69.44	$69.45	$69.40
Purchase #6	$106.74	4.263%	$111.2903	$111.29	$111.30	$111.30
Purchase #7	$86.47	10.220%	$95.3072	$95.31	$95.30	$95.30
7 purchase totals =	$715.60		$786.9246	$786.93	$786.95	$786.90