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	$170.31	4.805%	$178.4934	$178.49	$178.50	$178.50
Purchase #2	$32.50	10.394%	$35.8781	$35.88	$35.90	$35.90
Purchase #3	$15.75	11.746%	$17.6	$17.60	$17.60	$17.60
Purchase #4	$76.59	8.175%	$82.8512	$82.85	$82.85	$82.90
Purchase #5	$193.38	8.775%	$210.3491	$210.35	$210.35	$210.30
Purchase #6	$30.43	7.370%	$32.6727	$32.67	$32.65	$32.70
Purchase #7	$231.83	4.338%	$241.8868	$241.89	$241.90	$241.90
7 purchase totals =	$750.79		$799.7313	$799.73	$799.75	$799.80