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	$6.77	7.854%	$7.3017	$7.30	$7.30	$7.30
Purchase #2	$180.74	8.633%	$196.3433	$196.34	$196.35	$196.30
Purchase #3	$212.39	11.729%	$237.3012	$237.30	$237.30	$237.30
Purchase #4	$89.91	10.761%	$99.5852	$99.59	$99.60	$99.60
Purchase #5	$176.33	3.496%	$182.4945	$182.49	$182.50	$182.50
Purchase #6	$40.47	9.167%	$44.1799	$44.18	$44.20	$44.20
Purchase #7	$220.80	4.356%	$230.418	$230.42	$230.40	$230.40
7 purchase totals =	$927.41		$997.6238	$997.62	$997.65	$997.60