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	$232.99	6.721%	$248.6493	$248.65	$248.65	$248.60
Purchase #2	$86.71	4.349%	$90.481	$90.48	$90.50	$90.50
Purchase #3	$175.65	8.656%	$190.8543	$190.85	$190.85	$190.90
Purchase #4	$75.81	12.639%	$85.3916	$85.39	$85.40	$85.40
Purchase #5	$6.46	13.550%	$7.3353	$7.34	$7.35	$7.30
Purchase #6	$70.59	4.626%	$73.8555	$73.86	$73.85	$73.90
Purchase #7	$237.55	10.773%	$263.1413	$263.14	$263.15	$263.10
7 purchase totals =	$885.76		$959.7083	$959.71	$959.75	$959.70