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	$103.64	5.423%	$109.2604	$109.26	$109.25	$109.30
Purchase #2	$245.64	10.682%	$271.8793	$271.88	$271.90	$271.90
Purchase #3	$146.35	11.299%	$162.8861	$162.89	$162.90	$162.90
Purchase #4	$162.59	9.799%	$178.5222	$178.52	$178.50	$178.50
Purchase #5	$129.56	6.446%	$137.9114	$137.91	$137.90	$137.90
Purchase #6	$166.35	5.170%	$174.9503	$174.95	$174.95	$175.00
Purchase #7	$122.35	4.447%	$127.7909	$127.79	$127.80	$127.80
7 purchase totals =	$1,076.48		$1,163.2006	$1,163.20	$1,163.20	$1,163.30