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	$141.30	8.833%	$153.781	$153.78	$153.80	$153.80
Purchase #2	$40.35	7.435%	$43.35	$43.35	$43.35	$43.40
Purchase #3	$107.43	12.524%	$120.8845	$120.88	$120.90	$120.90
Purchase #4	$200.51	5.201%	$210.9385	$210.94	$210.95	$210.90
Purchase #5	$10.60	6.742%	$11.3147	$11.31	$11.30	$11.30
Purchase #6	$93.76	5.437%	$98.8577	$98.86	$98.85	$98.90
Purchase #7	$179.77	6.672%	$191.7643	$191.76	$191.75	$191.80
7 purchase totals =	$773.72		$830.8907	$830.88	$830.90	$831.00