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	$5.59	5.483%	$5.8965	$5.90	$5.90	$5.90
Purchase #2	$179.50	11.127%	$199.473	$199.47	$199.45	$199.50
Purchase #3	$228.43	5.158%	$240.2124	$240.21	$240.20	$240.20
Purchase #4	$250.84	4.799%	$262.8778	$262.88	$262.90	$262.90
Purchase #5	$23.88	6.168%	$25.3529	$25.35	$25.35	$25.40
Purchase #6	$137.96	6.824%	$147.3744	$147.37	$147.35	$147.40
Purchase #7	$241.65	11.444%	$269.3044	$269.30	$269.30	$269.30
7 purchase totals =	$1,067.85		$1,150.4914	$1,150.48	$1,150.45	$1,150.60