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	$72.82	13.316%	$82.5167	$82.52	$82.50	$82.50
Purchase #2	$126.48	6.565%	$134.7834	$134.78	$134.80	$134.80
Purchase #3	$195.95	3.453%	$202.7162	$202.72	$202.70	$202.70
Purchase #4	$165.92	12.452%	$186.5804	$186.58	$186.60	$186.60
Purchase #5	$50.40	5.792%	$53.3192	$53.32	$53.30	$53.30
Purchase #6	$92.72	8.481%	$100.5836	$100.58	$100.60	$100.60
Purchase #7	$140.76	11.250%	$156.5955	$156.60	$156.60	$156.60
7 purchase totals =	$845.05		$917.0950	$917.10	$917.10	$917.10