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	$229.53	7.872%	$247.5986	$247.60	$247.60	$247.60
Purchase #2	$195.60	5.563%	$206.4812	$206.48	$206.50	$206.50
Purchase #3	$214.64	4.167%	$223.584	$223.58	$223.60	$223.60
Purchase #4	$243.29	7.789%	$262.2399	$262.24	$262.25	$262.20
Purchase #5	$249.89	6.187%	$265.3507	$265.35	$265.35	$265.40
Purchase #6	$81.78	11.443%	$91.1381	$91.14	$91.15	$91.10
Purchase #7	$34.27	12.172%	$38.4413	$38.44	$38.45	$38.40
7 purchase totals =	$1,249.00		$1,334.8338	$1,334.83	$1,334.90	$1,334.80