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	$140.49	9.550%	$153.9068	$153.91	$153.90	$153.90
Purchase #2	$84.59	5.226%	$89.0107	$89.01	$89.00	$89.00
Purchase #3	$100.76	11.581%	$112.429	$112.43	$112.45	$112.40
Purchase #4	$61.93	6.161%	$65.7455	$65.75	$65.75	$65.70
Purchase #5	$7.47	5.801%	$7.9033	$7.90	$7.90	$7.90
Purchase #6	$9.74	8.533%	$10.5711	$10.57	$10.55	$10.60
Purchase #7	$62.89	9.437%	$68.8249	$68.82	$68.80	$68.80
7 purchase totals =	$467.87		$508.3913	$508.39	$508.35	$508.30