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	$29.51	13.699%	$33.5526	$33.55	$33.55	$33.60
Purchase #2	$208.57	3.481%	$215.8303	$215.83	$215.85	$215.80
Purchase #3	$138.34	12.652%	$155.8428	$155.84	$155.85	$155.80
Purchase #4	$215.90	13.873%	$245.8518	$245.85	$245.85	$245.90
Purchase #5	$54.36	8.286%	$58.8643	$58.86	$58.85	$58.90
Purchase #6	$175.95	11.535%	$196.2458	$196.25	$196.25	$196.20
Purchase #7	$229.54	9.336%	$250.9699	$250.97	$250.95	$251.00
7 purchase totals =	$1,052.17		$1,157.1575	$1,157.15	$1,157.15	$1,157.20