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	$250.42	12.521%	$281.7751	$281.78	$281.80	$281.80
Purchase #2	$29.99	3.620%	$31.0756	$31.08	$31.10	$31.10
Purchase #3	$22.60	13.192%	$25.5814	$25.58	$25.60	$25.60
Purchase #4	$218.90	12.446%	$246.1443	$246.14	$246.15	$246.10
Purchase #5	$241.48	3.632%	$250.2506	$250.25	$250.25	$250.30
Purchase #6	$92.26	13.380%	$104.6044	$104.60	$104.60	$104.60
Purchase #7	$148.29	3.104%	$152.8929	$152.89	$152.90	$152.90
7 purchase totals =	$1,003.94		$1,092.3243	$1,092.32	$1,092.40	$1,092.40