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	$71.49	13.340%	$81.0268	$81.03	$81.05	$81.00
Purchase #2	$128.38	7.864%	$138.4758	$138.48	$138.50	$138.50
Purchase #3	$86.81	10.784%	$96.1716	$96.17	$96.15	$96.20
Purchase #4	$210.89	11.109%	$234.3178	$234.32	$234.30	$234.30
Purchase #5	$180.58	4.455%	$188.6248	$188.62	$188.60	$188.60
Purchase #6	$156.78	12.459%	$176.3132	$176.31	$176.30	$176.30
Purchase #7	$55.62	6.469%	$59.2181	$59.22	$59.20	$59.20
7 purchase totals =	$890.55		$974.1481	$974.15	$974.10	$974.10