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	$70.75	11.556%	$78.9259	$78.93	$78.95	$78.90
Purchase #2	$57.60	12.274%	$64.6698	$64.67	$64.65	$64.70
Purchase #3	$92.82	8.587%	$100.7905	$100.79	$100.80	$100.80
Purchase #4	$161.47	6.474%	$171.9236	$171.92	$171.90	$171.90
Purchase #5	$90.85	9.269%	$99.2709	$99.27	$99.25	$99.30
Purchase #6	$157.36	12.394%	$176.8632	$176.86	$176.85	$176.90
Purchase #7	$27.30	3.828%	$28.345	$28.35	$28.35	$28.30
7 purchase totals =	$658.15		$720.7889	$720.79	$720.75	$720.80