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	$83.25	9.235%	$90.9381	$90.94	$90.95	$90.90
Purchase #2	$101.37	10.632%	$112.1477	$112.15	$112.15	$112.10
Purchase #3	$143.82	8.227%	$155.6521	$155.65	$155.65	$155.70
Purchase #4	$169.62	5.545%	$179.0254	$179.03	$179.05	$179.00
Purchase #5	$85.56	5.155%	$89.9706	$89.97	$89.95	$90.00
Purchase #6	$243.65	12.756%	$274.73	$274.73	$274.75	$274.70
Purchase #7	$11.80	6.399%	$12.5551	$12.56	$12.55	$12.60
7 purchase totals =	$839.07		$915.0190	$915.03	$915.05	$915.00