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	$95.95	4.774%	$100.5307	$100.53	$100.55	$100.50
Purchase #2	$176.60	8.180%	$191.0459	$191.05	$191.05	$191.00
Purchase #3	$80.71	13.744%	$91.8028	$91.80	$91.80	$91.80
Purchase #4	$59.96	4.270%	$62.5203	$62.52	$62.50	$62.50
Purchase #5	$82.43	9.349%	$90.1364	$90.14	$90.15	$90.10
Purchase #6	$88.30	5.326%	$93.0029	$93.00	$93.00	$93.00
Purchase #7	$158.67	7.413%	$170.4322	$170.43	$170.45	$170.40
7 purchase totals =	$742.62		$799.4712	$799.47	$799.50	$799.30