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	$71.33	13.556%	$80.9995	$81.00	$81.00	$81.00
Purchase #2	$168.59	3.282%	$174.1231	$174.12	$174.10	$174.10
Purchase #3	$86.29	13.477%	$97.9193	$97.92	$97.90	$97.90
Purchase #4	$24.40	12.627%	$27.481	$27.48	$27.50	$27.50
Purchase #5	$86.33	9.556%	$94.5797	$94.58	$94.60	$94.60
Purchase #6	$104.80	13.874%	$119.34	$119.34	$119.35	$119.30
Purchase #7	$39.93	13.577%	$45.3513	$45.35	$45.35	$45.40
7 purchase totals =	$581.67		$639.7939	$639.79	$639.80	$639.80