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	$231.91	4.841%	$243.1368	$243.14	$243.15	$243.10
Purchase #2	$21.96	13.436%	$24.9105	$24.91	$24.90	$24.90
Purchase #3	$72.73	10.259%	$80.1914	$80.19	$80.20	$80.20
Purchase #4	$208.64	12.603%	$234.9349	$234.93	$234.95	$234.90
Purchase #5	$59.57	4.460%	$62.2268	$62.23	$62.25	$62.20
Purchase #6	$124.46	7.262%	$133.4983	$133.50	$133.50	$133.50
Purchase #7	$52.25	13.462%	$59.2839	$59.28	$59.30	$59.30
7 purchase totals =	$771.52		$838.1826	$838.18	$838.25	$838.10