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	$20.82	5.846%	$22.0371	$22.04	$22.05	$22.00
Purchase #2	$97.29	7.705%	$104.7862	$104.79	$104.80	$104.80
Purchase #3	$53.45	7.780%	$57.6084	$57.61	$57.60	$57.60
Purchase #4	$158.72	13.452%	$180.071	$180.07	$180.05	$180.10
Purchase #5	$151.37	3.515%	$156.6907	$156.69	$156.70	$156.70
Purchase #6	$52.44	12.826%	$59.166	$59.17	$59.15	$59.20
Purchase #7	$109.59	6.697%	$116.9292	$116.93	$116.95	$116.90
7 purchase totals =	$643.68		$697.2886	$697.30	$697.30	$697.30