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	$11.81	11.820%	$13.2059	$13.21	$13.20	$13.20
Purchase #2	$31.87	9.752%	$34.978	$34.98	$35.00	$35.00
Purchase #3	$110.33	12.307%	$123.9083	$123.91	$123.90	$123.90
Purchase #4	$148.47	5.513%	$156.6552	$156.66	$156.65	$156.70
Purchase #5	$198.81	11.707%	$222.0847	$222.08	$222.10	$222.10
Purchase #6	$41.67	12.206%	$46.7562	$46.76	$46.75	$46.80
Purchase #7	$236.90	7.321%	$254.2434	$254.24	$254.25	$254.20
7 purchase totals =	$779.86		$851.8317	$851.84	$851.85	$851.90