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	$49.94	10.671%	$55.2691	$55.27	$55.25	$55.30
Purchase #2	$149.71	13.201%	$169.4732	$169.47	$169.45	$169.50
Purchase #3	$247.90	11.148%	$275.5359	$275.54	$275.55	$275.50
Purchase #4	$203.45	8.832%	$221.4187	$221.42	$221.40	$221.40
Purchase #5	$151.47	7.569%	$162.9348	$162.93	$162.95	$162.90
Purchase #6	$101.51	7.206%	$108.8248	$108.82	$108.80	$108.80
Purchase #7	$135.68	12.171%	$152.1936	$152.19	$152.20	$152.20
7 purchase totals =	$1,039.66		$1,145.6501	$1,145.64	$1,145.60	$1,145.60