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	$245.92	10.670%	$272.1597	$272.16	$272.15	$272.20
Purchase #2	$69.71	13.279%	$78.9668	$78.97	$78.95	$79.00
Purchase #3	$31.53	3.226%	$32.5472	$32.55	$32.55	$32.50
Purchase #4	$41.96	3.602%	$43.4714	$43.47	$43.45	$43.50
Purchase #5	$136.50	3.859%	$141.7675	$141.77	$141.75	$141.80
Purchase #6	$85.54	4.819%	$89.6622	$89.66	$89.65	$89.70
Purchase #7	$47.25	12.429%	$53.1227	$53.12	$53.10	$53.10
7 purchase totals =	$658.41		$711.6975	$711.70	$711.60	$711.80