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	$85.85	4.802%	$89.9725	$89.97	$89.95	$90.00
Purchase #2	$32.40	12.315%	$36.3901	$36.39	$36.40	$36.40
Purchase #3	$19.35	6.388%	$20.5861	$20.59	$20.60	$20.60
Purchase #4	$34.67	10.586%	$38.3402	$38.34	$38.35	$38.30
Purchase #5	$228.54	8.415%	$247.7716	$247.77	$247.75	$247.80
Purchase #6	$196.90	12.266%	$221.0518	$221.05	$221.05	$221.10
Purchase #7	$50.92	7.456%	$54.7166	$54.72	$54.70	$54.70
7 purchase totals =	$648.63		$708.8289	$708.83	$708.80	$708.90