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	$54.41	5.611%	$57.4629	$57.46	$57.45	$57.50
Purchase #2	$27.34	4.775%	$28.6455	$28.65	$28.65	$28.60
Purchase #3	$246.92	13.639%	$280.5974	$280.60	$280.60	$280.60
Purchase #4	$92.84	12.749%	$104.6762	$104.68	$104.70	$104.70
Purchase #5	$182.38	4.104%	$189.8649	$189.86	$189.85	$189.90
Purchase #6	$91.80	8.218%	$99.3441	$99.34	$99.35	$99.30
Purchase #7	$105.33	4.179%	$109.7317	$109.73	$109.75	$109.70
7 purchase totals =	$801.02		$870.3227	$870.32	$870.35	$870.30