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	$6.86	13.175%	$7.7638	$7.76	$7.75	$7.80
Purchase #2	$6.77	5.279%	$7.1274	$7.13	$7.15	$7.10
Purchase #3	$81.55	3.420%	$84.339	$84.34	$84.35	$84.30
Purchase #4	$53.80	7.110%	$57.6252	$57.63	$57.65	$57.60
Purchase #5	$90.75	10.781%	$100.5338	$100.53	$100.55	$100.50
Purchase #6	$98.58	6.377%	$104.8664	$104.87	$104.85	$104.90
Purchase #7	$100.92	12.418%	$113.4522	$113.45	$113.45	$113.50
7 purchase totals =	$439.23		$475.7078	$475.71	$475.75	$475.70