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	$84.62	7.151%	$90.6712	$90.67	$90.65	$90.70
Purchase #2	$88.94	12.278%	$99.8601	$99.86	$99.85	$99.90
Purchase #3	$147.89	4.855%	$155.0701	$155.07	$155.05	$155.10
Purchase #4	$153.59	11.297%	$170.9411	$170.94	$170.95	$170.90
Purchase #5	$170.67	12.326%	$191.7068	$191.71	$191.70	$191.70
Purchase #6	$157.59	4.541%	$164.7462	$164.75	$164.75	$164.70
Purchase #7	$73.84	11.554%	$82.3715	$82.37	$82.35	$82.40
7 purchase totals =	$877.14		$955.3670	$955.37	$955.30	$955.40