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	$51.53	6.542%	$54.9011	$54.90	$54.90	$54.90
Purchase #2	$46.57	9.163%	$50.8372	$50.84	$50.85	$50.80
Purchase #3	$27.69	6.609%	$29.52	$29.52	$29.50	$29.50
Purchase #4	$36.39	11.276%	$40.4933	$40.49	$40.50	$40.50
Purchase #5	$84.50	12.369%	$94.9518	$94.95	$94.95	$95.00
Purchase #6	$108.27	5.204%	$113.9044	$113.90	$113.90	$113.90
Purchase #7	$197.71	8.606%	$214.7249	$214.72	$214.70	$214.70
7 purchase totals =	$552.66		$599.3327	$599.32	$599.30	$599.30