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	$24.85	9.865%	$27.3015	$27.30	$27.30	$27.30
Purchase #2	$182.55	6.839%	$195.0346	$195.03	$195.05	$195.00
Purchase #3	$79.66	7.741%	$85.8265	$85.83	$85.85	$85.80
Purchase #4	$186.55	5.337%	$196.5062	$196.51	$196.50	$196.50
Purchase #5	$169.47	3.623%	$175.6099	$175.61	$175.60	$175.60
Purchase #6	$64.82	3.754%	$67.2533	$67.25	$67.25	$67.30
Purchase #7	$36.56	10.855%	$40.5286	$40.53	$40.55	$40.50
7 purchase totals =	$744.46		$788.0606	$788.06	$788.10	$788.00