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	$76.99	10.358%	$84.9646	$84.96	$84.95	$85.00
Purchase #2	$115.89	12.236%	$130.0703	$130.07	$130.05	$130.10
Purchase #3	$24.72	10.311%	$27.2689	$27.27	$27.25	$27.30
Purchase #4	$59.49	3.296%	$61.4508	$61.45	$61.45	$61.50
Purchase #5	$186.78	7.219%	$200.2636	$200.26	$200.25	$200.30
Purchase #6	$168.59	6.139%	$178.9397	$178.94	$178.95	$178.90
Purchase #7	$49.30	6.135%	$52.3246	$52.32	$52.30	$52.30
7 purchase totals =	$681.76		$735.2825	$735.27	$735.20	$735.40