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	$247.84	4.252%	$258.3782	$258.38	$258.40	$258.40
Purchase #2	$182.37	9.615%	$199.9049	$199.90	$199.90	$199.90
Purchase #3	$45.50	10.848%	$50.4358	$50.44	$50.45	$50.40
Purchase #4	$208.55	3.135%	$215.088	$215.09	$215.10	$215.10
Purchase #5	$146.29	7.110%	$156.6912	$156.69	$156.70	$156.70
Purchase #6	$110.38	11.730%	$123.3276	$123.33	$123.35	$123.30
Purchase #7	$172.66	7.420%	$185.4714	$185.47	$185.45	$185.50
7 purchase totals =	$1,113.59		$1,189.2971	$1,189.30	$1,189.35	$1,189.30