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	$121.51	5.241%	$127.8783	$127.88	$127.90	$127.90
Purchase #2	$115.66	9.706%	$126.886	$126.89	$126.90	$126.90
Purchase #3	$90.45	8.596%	$98.2251	$98.23	$98.25	$98.20
Purchase #4	$46.80	6.801%	$49.9829	$49.98	$50.00	$50.00
Purchase #5	$204.51	10.638%	$226.2658	$226.27	$226.25	$226.30
Purchase #6	$205.76	3.661%	$213.2929	$213.29	$213.30	$213.30
Purchase #7	$35.91	12.235%	$40.3036	$40.30	$40.30	$40.30
7 purchase totals =	$820.60		$882.8346	$882.84	$882.90	$882.90