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	$31.73	8.726%	$34.4988	$34.50	$34.50	$34.50
Purchase #2	$224.96	8.658%	$244.437	$244.44	$244.45	$244.40
Purchase #3	$77.67	6.187%	$82.4754	$82.48	$82.50	$82.50
Purchase #4	$80.55	10.203%	$88.7685	$88.77	$88.75	$88.80
Purchase #5	$31.94	12.268%	$35.8584	$35.86	$35.85	$35.90
Purchase #6	$126.31	8.871%	$137.515	$137.52	$137.50	$137.50
Purchase #7	$245.54	12.597%	$276.4707	$276.47	$276.45	$276.50
7 purchase totals =	$818.70		$900.0238	$900.04	$900.00	$900.10