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	$122.82	12.300%	$137.9269	$137.93	$137.95	$137.90
Purchase #2	$212.82	9.792%	$233.6593	$233.66	$233.65	$233.70
Purchase #3	$85.58	6.185%	$90.8731	$90.87	$90.85	$90.90
Purchase #4	$153.79	8.122%	$166.2808	$166.28	$166.30	$166.30
Purchase #5	$26.76	5.264%	$28.1686	$28.17	$28.15	$28.20
Purchase #6	$40.44	10.711%	$44.7715	$44.77	$44.75	$44.80
Purchase #7	$218.66	9.538%	$239.5158	$239.52	$239.50	$239.50
7 purchase totals =	$860.87		$941.1960	$941.20	$941.15	$941.30