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	$137.46	3.364%	$142.0842	$142.08	$142.10	$142.10
Purchase #2	$135.35	8.250%	$146.5164	$146.52	$146.50	$146.50
Purchase #3	$139.79	9.576%	$153.1763	$153.18	$153.20	$153.20
Purchase #4	$34.56	6.320%	$36.7442	$36.74	$36.75	$36.70
Purchase #5	$51.72	9.857%	$56.818	$56.82	$56.80	$56.80
Purchase #6	$149.43	11.319%	$166.344	$166.34	$166.35	$166.30
Purchase #7	$113.69	8.689%	$123.5685	$123.57	$123.55	$123.60
7 purchase totals =	$762.00		$825.2516	$825.25	$825.25	$825.20