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	$5.30	11.794%	$5.9251	$5.93	$5.95	$5.90
Purchase #2	$73.90	6.351%	$78.5934	$78.59	$78.60	$78.60
Purchase #3	$228.82	11.775%	$255.7636	$255.76	$255.75	$255.80
Purchase #4	$245.70	11.730%	$274.5206	$274.52	$274.50	$274.50
Purchase #5	$178.94	7.141%	$191.7181	$191.72	$191.70	$191.70
Purchase #6	$161.84	6.645%	$172.5943	$172.59	$172.60	$172.60
Purchase #7	$97.45	8.207%	$105.4477	$105.45	$105.45	$105.40
7 purchase totals =	$991.95		$1,084.5628	$1,084.56	$1,084.55	$1,084.50