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	$94.45	5.717%	$99.8497	$99.85	$99.85	$99.80
Purchase #2	$150.36	4.467%	$157.0766	$157.08	$157.10	$157.10
Purchase #3	$246.78	5.544%	$260.4615	$260.46	$260.45	$260.50
Purchase #4	$88.38	3.147%	$91.1613	$91.16	$91.15	$91.20
Purchase #5	$205.61	4.659%	$215.1894	$215.19	$215.20	$215.20
Purchase #6	$90.30	10.233%	$99.5404	$99.54	$99.55	$99.50
Purchase #7	$31.54	3.647%	$32.6903	$32.69	$32.70	$32.70
7 purchase totals =	$907.42		$955.9692	$955.97	$956.00	$956.00