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	$28.42	9.586%	$31.1443	$31.14	$31.15	$31.10
Purchase #2	$87.90	13.482%	$99.7507	$99.75	$99.75	$99.80
Purchase #3	$159.50	11.484%	$177.817	$177.82	$177.80	$177.80
Purchase #4	$89.39	10.510%	$98.7849	$98.78	$98.80	$98.80
Purchase #5	$72.80	10.237%	$80.2525	$80.25	$80.25	$80.30
Purchase #6	$94.85	5.307%	$99.8837	$99.88	$99.90	$99.90
Purchase #7	$173.88	8.713%	$189.0302	$189.03	$189.05	$189.00
7 purchase totals =	$706.74		$776.6633	$776.65	$776.70	$776.70