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	$20.77	6.331%	$22.0849	$22.08	$22.10	$22.10
Purchase #2	$121.41	12.448%	$136.5231	$136.52	$136.50	$136.50
Purchase #3	$82.29	5.209%	$86.5765	$86.58	$86.60	$86.60
Purchase #4	$108.32	3.743%	$112.3744	$112.37	$112.35	$112.40
Purchase #5	$131.60	12.290%	$147.7736	$147.77	$147.75	$147.80
Purchase #6	$25.71	7.799%	$27.7151	$27.72	$27.70	$27.70
Purchase #7	$81.56	4.550%	$85.271	$85.27	$85.25	$85.30
7 purchase totals =	$571.66		$618.3186	$618.31	$618.25	$618.40