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	$133.89	10.220%	$147.5736	$147.57	$147.55	$147.60
Purchase #2	$99.47	12.521%	$111.9246	$111.92	$111.90	$111.90
Purchase #3	$144.90	11.284%	$161.2505	$161.25	$161.25	$161.30
Purchase #4	$232.59	9.838%	$255.4722	$255.47	$255.45	$255.50
Purchase #5	$176.91	12.471%	$198.9724	$198.97	$198.95	$199.00
Purchase #6	$30.64	6.629%	$32.6711	$32.67	$32.65	$32.70
Purchase #7	$85.89	4.366%	$89.64	$89.64	$89.65	$89.60
7 purchase totals =	$904.29		$997.5044	$997.49	$997.40	$997.60