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	$34.77	10.189%	$38.3127	$38.31	$38.30	$38.30
Purchase #2	$85.64	10.540%	$94.6665	$94.67	$94.65	$94.70
Purchase #3	$41.98	10.721%	$46.4807	$46.48	$46.50	$46.50
Purchase #4	$205.55	9.847%	$225.7905	$225.79	$225.80	$225.80
Purchase #5	$96.29	5.199%	$101.2961	$101.30	$101.30	$101.30
Purchase #6	$91.86	3.228%	$94.8252	$94.83	$94.85	$94.80
Purchase #7	$64.58	5.158%	$67.911	$67.91	$67.90	$67.90
7 purchase totals =	$620.67		$669.2827	$669.29	$669.30	$669.30