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	$7.42	6.736%	$7.9198	$7.92	$7.90	$7.90
Purchase #2	$37.63	8.826%	$40.9512	$40.95	$40.95	$41.00
Purchase #3	$12.47	10.224%	$13.7449	$13.74	$13.75	$13.70
Purchase #4	$32.77	5.270%	$34.497	$34.50	$34.50	$34.50
Purchase #5	$200.36	6.584%	$213.5517	$213.55	$213.55	$213.60
Purchase #6	$180.90	5.872%	$191.5224	$191.52	$191.50	$191.50
Purchase #7	$119.72	12.248%	$134.3833	$134.38	$134.40	$134.40
7 purchase totals =	$591.27		$636.5703	$636.56	$636.55	$636.60