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	$240.65	7.367%	$258.3787	$258.38	$258.40	$258.40
Purchase #2	$75.72	12.264%	$85.0063	$85.01	$85.00	$85.00
Purchase #3	$190.27	3.282%	$196.5147	$196.51	$196.50	$196.50
Purchase #4	$149.95	8.649%	$162.9192	$162.92	$162.90	$162.90
Purchase #5	$162.51	3.208%	$167.7233	$167.72	$167.70	$167.70
Purchase #6	$212.55	10.795%	$235.4948	$235.49	$235.50	$235.50
Purchase #7	$25.75	7.258%	$27.6189	$27.62	$27.60	$27.60
7 purchase totals =	$1,057.40		$1,133.6559	$1,133.65	$1,133.60	$1,133.60