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	$144.97	8.224%	$156.8923	$156.89	$156.90	$156.90
Purchase #2	$29.81	5.267%	$31.3801	$31.38	$31.40	$31.40
Purchase #3	$200.31	12.850%	$226.0498	$226.05	$226.05	$226.00
Purchase #4	$166.78	8.596%	$181.1164	$181.12	$181.10	$181.10
Purchase #5	$35.73	12.194%	$40.0869	$40.09	$40.10	$40.10
Purchase #6	$117.82	4.800%	$123.4754	$123.48	$123.50	$123.50
Purchase #7	$74.90	13.158%	$84.7553	$84.76	$84.75	$84.80
7 purchase totals =	$770.32		$843.7562	$843.77	$843.80	$843.80