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	$52.96	10.189%	$58.3561	$58.36	$58.35	$58.40
Purchase #2	$190.51	3.164%	$196.5377	$196.54	$196.55	$196.50
Purchase #3	$123.96	8.857%	$134.9391	$134.94	$134.95	$134.90
Purchase #4	$43.83	3.263%	$45.2602	$45.26	$45.25	$45.30
Purchase #5	$82.84	3.285%	$85.5613	$85.56	$85.55	$85.60
Purchase #6	$235.62	9.527%	$258.0675	$258.07	$258.05	$258.10
Purchase #7	$27.61	9.747%	$30.3011	$30.30	$30.30	$30.30
7 purchase totals =	$757.33		$809.0230	$809.03	$809.00	$809.10