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	$94.31	6.317%	$100.2676	$100.27	$100.25	$100.30
Purchase #2	$16.63	3.328%	$17.1834	$17.18	$17.20	$17.20
Purchase #3	$112.75	3.523%	$116.7222	$116.72	$116.70	$116.70
Purchase #4	$105.37	6.184%	$111.8861	$111.89	$111.90	$111.90
Purchase #5	$119.78	6.868%	$128.0065	$128.01	$128.00	$128.00
Purchase #6	$92.91	3.394%	$96.0634	$96.06	$96.05	$96.10
Purchase #7	$30.44	9.774%	$33.4152	$33.42	$33.40	$33.40
7 purchase totals =	$572.19		$603.5444	$603.55	$603.50	$603.60