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	$19.76	4.523%	$20.6537	$20.65	$20.65	$20.70
Purchase #2	$103.83	5.460%	$109.4991	$109.50	$109.50	$109.50
Purchase #3	$218.88	10.586%	$242.0506	$242.05	$242.05	$242.10
Purchase #4	$31.29	5.322%	$32.9553	$32.96	$32.95	$33.00
Purchase #5	$133.51	4.122%	$139.0133	$139.01	$139.00	$139.00
Purchase #6	$140.38	4.296%	$146.4107	$146.41	$146.40	$146.40
Purchase #7	$158.43	6.393%	$168.5584	$168.56	$168.55	$168.60
7 purchase totals =	$806.08		$859.1411	$859.14	$859.10	$859.30