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	$249.46	12.195%	$279.8816	$279.88	$279.90	$279.90
Purchase #2	$43.33	13.771%	$49.297	$49.30	$49.30	$49.30
Purchase #3	$242.88	6.540%	$258.7644	$258.76	$258.75	$258.80
Purchase #4	$113.82	6.690%	$121.4346	$121.43	$121.45	$121.40
Purchase #5	$220.84	3.188%	$227.8804	$227.88	$227.90	$227.90
Purchase #6	$72.64	7.588%	$78.1519	$78.15	$78.15	$78.20
Purchase #7	$174.56	12.771%	$196.8531	$196.85	$196.85	$196.90
7 purchase totals =	$1,117.53		$1,212.2630	$1,212.25	$1,212.30	$1,212.40