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	$104.81	6.115%	$111.2191	$111.22	$111.20	$111.20
Purchase #2	$137.31	10.797%	$152.1354	$152.14	$152.15	$152.10
Purchase #3	$188.59	10.748%	$208.8597	$208.86	$208.85	$208.90
Purchase #4	$141.56	10.780%	$156.8202	$156.82	$156.80	$156.80
Purchase #5	$34.59	11.854%	$38.6903	$38.69	$38.70	$38.70
Purchase #6	$142.58	9.470%	$156.0823	$156.08	$156.10	$156.10
Purchase #7	$89.25	10.180%	$98.3357	$98.34	$98.35	$98.30
7 purchase totals =	$838.69		$922.1427	$922.15	$922.15	$922.10