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	$123.51	4.281%	$128.7975	$128.80	$128.80	$128.80
Purchase #2	$106.67	5.360%	$112.3875	$112.39	$112.40	$112.40
Purchase #3	$130.98	10.772%	$145.0892	$145.09	$145.10	$145.10
Purchase #4	$166.73	10.855%	$184.8285	$184.83	$184.85	$184.80
Purchase #5	$76.65	13.393%	$86.9157	$86.92	$86.90	$86.90
Purchase #6	$7.43	6.387%	$7.9046	$7.90	$7.90	$7.90
Purchase #7	$166.66	11.480%	$185.7926	$185.79	$185.80	$185.80
7 purchase totals =	$778.63		$851.7156	$851.72	$851.75	$851.70