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	$138.45	13.219%	$156.7517	$156.75	$156.75	$156.80
Purchase #2	$7.66	4.406%	$7.9975	$8.00	$8.00	$8.00
Purchase #3	$119.48	9.644%	$131.0027	$131.00	$131.00	$131.00
Purchase #4	$101.46	4.137%	$105.6574	$105.66	$105.65	$105.70
Purchase #5	$200.94	11.274%	$223.594	$223.59	$223.60	$223.60
Purchase #6	$157.42	4.566%	$164.6078	$164.61	$164.60	$164.60
Purchase #7	$244.36	9.586%	$267.7843	$267.78	$267.80	$267.80
7 purchase totals =	$969.77		$1,057.3954	$1,057.39	$1,057.40	$1,057.50