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	$110.85	4.158%	$115.4591	$115.46	$115.45	$115.50
Purchase #2	$28.39	12.769%	$32.0151	$32.02	$32.00	$32.00
Purchase #3	$140.29	10.757%	$155.381	$155.38	$155.40	$155.40
Purchase #4	$190.53	8.322%	$206.3859	$206.39	$206.40	$206.40
Purchase #5	$129.91	10.253%	$143.2297	$143.23	$143.25	$143.20
Purchase #6	$123.40	10.618%	$136.5026	$136.50	$136.50	$136.50
Purchase #7	$63.30	13.586%	$71.8999	$71.90	$71.90	$71.90
7 purchase totals =	$786.67		$860.8733	$860.88	$860.90	$860.90