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	$59.75	13.647%	$67.9041	$67.90	$67.90	$67.90
Purchase #2	$54.63	8.569%	$59.3112	$59.31	$59.30	$59.30
Purchase #3	$134.61	13.439%	$152.7002	$152.70	$152.70	$152.70
Purchase #4	$160.42	8.456%	$173.9851	$173.99	$174.00	$174.00
Purchase #5	$95.26	7.827%	$102.716	$102.72	$102.70	$102.70
Purchase #6	$135.84	10.651%	$150.3083	$150.31	$150.30	$150.30
Purchase #7	$99.35	13.617%	$112.8785	$112.88	$112.90	$112.90
7 purchase totals =	$739.86		$819.8034	$819.81	$819.80	$819.80