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	$75.82	12.619%	$85.3877	$85.39	$85.40	$85.40
Purchase #2	$70.86	7.314%	$76.0427	$76.04	$76.05	$76.00
Purchase #3	$154.58	5.232%	$162.6676	$162.67	$162.65	$162.70
Purchase #4	$184.51	6.694%	$196.8611	$196.86	$196.85	$196.90
Purchase #5	$213.75	9.867%	$234.8407	$234.84	$234.85	$234.80
Purchase #6	$117.83	13.601%	$133.8561	$133.86	$133.85	$133.90
Purchase #7	$171.48	5.390%	$180.7228	$180.72	$180.70	$180.70
7 purchase totals =	$988.83		$1,070.3787	$1,070.38	$1,070.35	$1,070.40