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	$45.89	12.320%	$51.5436	$51.54	$51.55	$51.50
Purchase #2	$49.65	12.454%	$55.8334	$55.83	$55.85	$55.80
Purchase #3	$21.50	5.263%	$22.6315	$22.63	$22.65	$22.60
Purchase #4	$195.28	7.673%	$210.2638	$210.26	$210.25	$210.30
Purchase #5	$183.43	7.368%	$196.9451	$196.95	$196.95	$196.90
Purchase #6	$72.60	13.582%	$82.4605	$82.46	$82.45	$82.50
Purchase #7	$198.78	13.839%	$226.2892	$226.29	$226.30	$226.30
7 purchase totals =	$767.13		$845.9671	$845.96	$846.00	$845.90