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	$56.67	12.753%	$63.8971	$63.90	$63.90	$63.90
Purchase #2	$225.56	7.438%	$242.3372	$242.34	$242.35	$242.30
Purchase #3	$186.68	9.201%	$203.8564	$203.86	$203.85	$203.90
Purchase #4	$78.83	9.452%	$86.281	$86.28	$86.30	$86.30
Purchase #5	$16.85	11.462%	$18.7813	$18.78	$18.80	$18.80
Purchase #6	$139.39	13.781%	$158.5993	$158.60	$158.60	$158.60
Purchase #7	$109.71	12.486%	$123.4084	$123.41	$123.40	$123.40
7 purchase totals =	$813.69		$897.1607	$897.17	$897.20	$897.20