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	$235.47	6.309%	$250.3258	$250.33	$250.35	$250.30
Purchase #2	$182.39	12.523%	$205.2307	$205.23	$205.25	$205.20
Purchase #3	$42.50	9.563%	$46.5643	$46.56	$46.55	$46.60
Purchase #4	$245.88	7.761%	$264.9627	$264.96	$264.95	$265.00
Purchase #5	$20.78	13.103%	$23.5028	$23.50	$23.50	$23.50
Purchase #6	$86.77	4.116%	$90.3415	$90.34	$90.35	$90.30
Purchase #7	$244.90	10.524%	$270.6733	$270.67	$270.65	$270.70
7 purchase totals =	$1,058.69		$1,151.6011	$1,151.59	$1,151.60	$1,151.60