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	$89.57	12.151%	$100.4537	$100.45	$100.45	$100.50
Purchase #2	$86.98	12.570%	$97.9134	$97.91	$97.90	$97.90
Purchase #3	$113.93	9.158%	$124.3637	$124.36	$124.35	$124.40
Purchase #4	$134.48	8.714%	$146.1986	$146.20	$146.20	$146.20
Purchase #5	$147.39	12.365%	$165.6148	$165.61	$165.60	$165.60
Purchase #6	$193.74	3.464%	$200.4512	$200.45	$200.45	$200.50
Purchase #7	$36.87	12.738%	$41.5665	$41.57	$41.55	$41.60
7 purchase totals =	$802.96		$876.5619	$876.55	$876.50	$876.70