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	$34.52	11.673%	$38.5495	$38.55	$38.55	$38.50
Purchase #2	$241.38	13.806%	$274.7049	$274.70	$274.70	$274.70
Purchase #3	$167.54	13.127%	$189.533	$189.53	$189.55	$189.50
Purchase #4	$78.36	5.739%	$82.8571	$82.86	$82.85	$82.90
Purchase #5	$119.43	7.491%	$128.3765	$128.38	$128.40	$128.40
Purchase #6	$122.32	4.270%	$127.5431	$127.54	$127.55	$127.50
Purchase #7	$221.64	8.438%	$240.342	$240.34	$240.35	$240.30
7 purchase totals =	$985.19		$1,081.9061	$1,081.90	$1,081.95	$1,081.80