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	$126.34	10.788%	$139.9696	$139.97	$139.95	$140.00
Purchase #2	$95.30	12.334%	$107.0543	$107.05	$107.05	$107.10
Purchase #3	$205.98	12.377%	$231.4741	$231.47	$231.45	$231.50
Purchase #4	$168.96	13.535%	$191.8287	$191.83	$191.85	$191.80
Purchase #5	$90.46	10.408%	$99.8751	$99.88	$99.90	$99.90
Purchase #6	$11.62	4.749%	$12.1718	$12.17	$12.15	$12.20
Purchase #7	$16.88	13.696%	$19.1919	$19.19	$19.20	$19.20
7 purchase totals =	$715.54		$801.5655	$801.56	$801.55	$801.70