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	$27.35	5.339%	$28.8102	$28.81	$28.80	$28.80
Purchase #2	$250.58	7.625%	$269.6867	$269.69	$269.70	$269.70
Purchase #3	$35.40	11.197%	$39.3637	$39.36	$39.35	$39.40
Purchase #4	$72.65	7.670%	$78.2223	$78.22	$78.20	$78.20
Purchase #5	$54.54	8.472%	$59.1606	$59.16	$59.15	$59.20
Purchase #6	$198.46	10.661%	$219.6178	$219.62	$219.60	$219.60
Purchase #7	$38.88	11.551%	$43.371	$43.37	$43.35	$43.40
7 purchase totals =	$677.86		$738.2323	$738.23	$738.15	$738.30