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	$216.84	13.668%	$246.4777	$246.48	$246.50	$246.50
Purchase #2	$78.71	6.555%	$83.8694	$83.87	$83.85	$83.90
Purchase #3	$164.74	13.259%	$186.5829	$186.58	$186.60	$186.60
Purchase #4	$90.90	6.315%	$96.6403	$96.64	$96.65	$96.60
Purchase #5	$58.35	8.372%	$63.2351	$63.24	$63.25	$63.20
Purchase #6	$248.80	13.724%	$282.9453	$282.95	$282.95	$282.90
Purchase #7	$85.31	6.155%	$90.5608	$90.56	$90.55	$90.60
7 purchase totals =	$943.65		$1,050.3115	$1,050.32	$1,050.35	$1,050.30