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	$20.34	7.636%	$21.8932	$21.89	$21.90	$21.90
Purchase #2	$72.35	8.207%	$78.2878	$78.29	$78.30	$78.30
Purchase #3	$104.94	12.631%	$118.195	$118.20	$118.20	$118.20
Purchase #4	$163.69	7.851%	$176.5413	$176.54	$176.55	$176.50
Purchase #5	$82.65	3.873%	$85.851	$85.85	$85.85	$85.90
Purchase #6	$222.25	3.423%	$229.8576	$229.86	$229.85	$229.90
Purchase #7	$180.54	5.465%	$190.4065	$190.41	$190.40	$190.40
7 purchase totals =	$846.76		$901.0324	$901.04	$901.05	$901.10