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	$83.35	9.507%	$91.2741	$91.27	$91.25	$91.30
Purchase #2	$156.28	5.516%	$164.9004	$164.90	$164.90	$164.90
Purchase #3	$161.94	3.677%	$167.8945	$167.89	$167.90	$167.90
Purchase #4	$120.53	11.127%	$133.9414	$133.94	$133.95	$133.90
Purchase #5	$97.49	6.537%	$103.8629	$103.86	$103.85	$103.90
Purchase #6	$92.42	8.223%	$100.0197	$100.02	$100.00	$100.00
Purchase #7	$15.68	7.661%	$16.8812	$16.88	$16.90	$16.90
7 purchase totals =	$727.69		$778.7742	$778.76	$778.75	$778.80