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	$166.71	12.392%	$187.3687	$187.37	$187.35	$187.40
Purchase #2	$56.34	11.416%	$62.7718	$62.77	$62.75	$62.80
Purchase #3	$21.63	4.183%	$22.5348	$22.53	$22.55	$22.50
Purchase #4	$83.51	8.286%	$90.4296	$90.43	$90.45	$90.40
Purchase #5	$80.37	12.269%	$90.2306	$90.23	$90.25	$90.20
Purchase #6	$250.25	12.590%	$281.7565	$281.76	$281.75	$281.80
Purchase #7	$195.44	11.458%	$217.8335	$217.83	$217.85	$217.80
7 purchase totals =	$854.25		$952.9255	$952.92	$952.95	$952.90