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	$26.79	7.842%	$28.8909	$28.89	$28.90	$28.90
Purchase #2	$41.46	5.370%	$43.6864	$43.69	$43.70	$43.70
Purchase #3	$154.51	5.331%	$162.7469	$162.75	$162.75	$162.70
Purchase #4	$217.64	9.584%	$238.4986	$238.50	$238.50	$238.50
Purchase #5	$97.41	4.545%	$101.8373	$101.84	$101.85	$101.80
Purchase #6	$119.85	6.624%	$127.7889	$127.79	$127.80	$127.80
Purchase #7	$223.55	11.782%	$249.8887	$249.89	$249.90	$249.90
7 purchase totals =	$881.21		$953.3377	$953.35	$953.40	$953.30