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	$55.74	7.167%	$59.7349	$59.73	$59.75	$59.70
Purchase #2	$237.41	9.765%	$260.5931	$260.59	$260.60	$260.60
Purchase #3	$152.32	11.376%	$169.6479	$169.65	$169.65	$169.60
Purchase #4	$215.25	3.231%	$222.2047	$222.20	$222.20	$222.20
Purchase #5	$54.46	9.440%	$59.601	$59.60	$59.60	$59.60
Purchase #6	$177.86	5.240%	$187.1799	$187.18	$187.20	$187.20
Purchase #7	$18.90	3.660%	$19.5917	$19.59	$19.60	$19.60
7 purchase totals =	$911.94		$978.5532	$978.54	$978.60	$978.50