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	$120.96	5.603%	$127.7374	$127.74	$127.75	$127.70
Purchase #2	$33.99	13.572%	$38.6031	$38.60	$38.60	$38.60
Purchase #3	$154.85	12.874%	$174.7854	$174.79	$174.80	$174.80
Purchase #4	$85.37	3.810%	$88.6226	$88.62	$88.60	$88.60
Purchase #5	$127.36	10.874%	$141.2091	$141.21	$141.20	$141.20
Purchase #6	$246.69	4.302%	$257.3026	$257.30	$257.30	$257.30
Purchase #7	$234.64	8.824%	$255.3446	$255.34	$255.35	$255.30
7 purchase totals =	$1,003.86		$1,083.6048	$1,083.60	$1,083.60	$1,083.50