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	$101.57	7.193%	$108.8759	$108.88	$108.90	$108.90
Purchase #2	$104.38	13.539%	$118.512	$118.51	$118.50	$118.50
Purchase #3	$77.66	3.296%	$80.2197	$80.22	$80.20	$80.20
Purchase #4	$148.82	12.325%	$167.1621	$167.16	$167.15	$167.20
Purchase #5	$72.89	13.149%	$82.4743	$82.47	$82.45	$82.50
Purchase #6	$56.97	11.171%	$63.3341	$63.33	$63.35	$63.30
Purchase #7	$109.46	11.184%	$121.702	$121.70	$121.70	$121.70
7 purchase totals =	$671.75		$742.2801	$742.27	$742.25	$742.30