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	$148.41	6.795%	$158.4945	$158.49	$158.50	$158.50
Purchase #2	$67.45	7.338%	$72.3995	$72.40	$72.40	$72.40
Purchase #3	$86.36	5.805%	$91.3732	$91.37	$91.35	$91.40
Purchase #4	$146.41	5.376%	$154.281	$154.28	$154.30	$154.30
Purchase #5	$200.93	13.499%	$228.0535	$228.05	$228.05	$228.10
Purchase #6	$106.72	11.564%	$119.0611	$119.06	$119.05	$119.10
Purchase #7	$29.30	12.288%	$32.9004	$32.90	$32.90	$32.90
7 purchase totals =	$785.58		$856.5632	$856.55	$856.55	$856.70