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	$190.60	13.608%	$216.5368	$216.54	$216.55	$216.50
Purchase #2	$235.72	13.400%	$267.3065	$267.31	$267.30	$267.30
Purchase #3	$94.85	11.559%	$105.8137	$105.81	$105.80	$105.80
Purchase #4	$40.55	5.802%	$42.9027	$42.90	$42.90	$42.90
Purchase #5	$123.64	6.774%	$132.0154	$132.02	$132.00	$132.00
Purchase #6	$239.51	11.709%	$267.5542	$267.55	$267.55	$267.60
Purchase #7	$184.90	13.210%	$209.3253	$209.33	$209.35	$209.30
7 purchase totals =	$1,109.77		$1,241.4546	$1,241.46	$1,241.45	$1,241.40