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	$88.33	12.538%	$99.4048	$99.40	$99.40	$99.40
Purchase #2	$33.76	6.242%	$35.8673	$35.87	$35.85	$35.90
Purchase #3	$145.79	3.523%	$150.9262	$150.93	$150.95	$150.90
Purchase #4	$43.69	5.191%	$45.9579	$45.96	$45.95	$46.00
Purchase #5	$240.42	11.129%	$267.1763	$267.18	$267.20	$267.20
Purchase #6	$222.88	13.874%	$253.8024	$253.80	$253.80	$253.80
Purchase #7	$214.56	11.606%	$239.4618	$239.46	$239.45	$239.50
7 purchase totals =	$989.43		$1,092.5967	$1,092.60	$1,092.60	$1,092.70