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	$141.83	6.409%	$150.9199	$150.92	$150.90	$150.90
Purchase #2	$88.90	3.146%	$91.6968	$91.70	$91.70	$91.70
Purchase #3	$28.63	10.677%	$31.6868	$31.69	$31.70	$31.70
Purchase #4	$81.50	10.373%	$89.954	$89.95	$89.95	$90.00
Purchase #5	$59.84	10.752%	$66.274	$66.27	$66.25	$66.30
Purchase #6	$217.99	8.737%	$237.0358	$237.04	$237.05	$237.00
Purchase #7	$172.74	10.822%	$191.4339	$191.43	$191.45	$191.40
7 purchase totals =	$791.43		$859.0012	$859.00	$859.00	$859.00