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	$79.37	13.240%	$89.8786	$89.88	$89.90	$89.90
Purchase #2	$191.75	7.162%	$205.4831	$205.48	$205.50	$205.50
Purchase #3	$82.77	9.828%	$90.9046	$90.90	$90.90	$90.90
Purchase #4	$61.28	10.534%	$67.7352	$67.74	$67.75	$67.70
Purchase #5	$94.38	5.713%	$99.7719	$99.77	$99.75	$99.80
Purchase #6	$22.50	8.611%	$24.4375	$24.44	$24.45	$24.40
Purchase #7	$126.41	3.662%	$131.0391	$131.04	$131.05	$131.00
7 purchase totals =	$658.46		$709.2500	$709.25	$709.30	$709.20