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	$126.55	10.544%	$139.8934	$139.89	$139.90	$139.90
Purchase #2	$43.50	3.657%	$45.0908	$45.09	$45.10	$45.10
Purchase #3	$85.95	11.760%	$96.0577	$96.06	$96.05	$96.10
Purchase #4	$130.32	6.820%	$139.2078	$139.21	$139.20	$139.20
Purchase #5	$194.37	7.454%	$208.8583	$208.86	$208.85	$208.90
Purchase #6	$83.81	4.864%	$87.8865	$87.89	$87.90	$87.90
Purchase #7	$113.30	10.607%	$125.3177	$125.32	$125.30	$125.30
7 purchase totals =	$777.80		$842.3122	$842.32	$842.30	$842.40