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	$155.87	10.198%	$171.7656	$171.77	$171.75	$171.80
Purchase #2	$40.45	6.636%	$43.1343	$43.13	$43.15	$43.10
Purchase #3	$156.36	7.342%	$167.84	$167.84	$167.85	$167.80
Purchase #4	$30.55	6.154%	$32.43	$32.43	$32.45	$32.40
Purchase #5	$38.31	11.666%	$42.7792	$42.78	$42.80	$42.80
Purchase #6	$159.78	5.291%	$168.234	$168.23	$168.25	$168.20
Purchase #7	$48.60	6.860%	$51.934	$51.93	$51.95	$51.90
7 purchase totals =	$629.92		$678.1171	$678.11	$678.20	$678.00