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	$68.56	12.832%	$77.3576	$77.36	$77.35	$77.40
Purchase #2	$163.58	9.737%	$179.5078	$179.51	$179.50	$179.50
Purchase #3	$63.31	11.465%	$70.5685	$70.57	$70.55	$70.60
Purchase #4	$136.43	11.758%	$152.4714	$152.47	$152.45	$152.50
Purchase #5	$105.79	7.187%	$113.3931	$113.39	$113.40	$113.40
Purchase #6	$47.30	4.803%	$49.5718	$49.57	$49.55	$49.60
Purchase #7	$18.92	8.818%	$20.5884	$20.59	$20.60	$20.60
7 purchase totals =	$603.89		$663.4586	$663.46	$663.40	$663.60