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	$247.81	7.143%	$265.5111	$265.51	$265.50	$265.50
Purchase #2	$100.75	5.287%	$106.0767	$106.08	$106.10	$106.10
Purchase #3	$50.75	13.383%	$57.5419	$57.54	$57.55	$57.50
Purchase #4	$136.82	13.181%	$154.8542	$154.85	$154.85	$154.90
Purchase #5	$190.85	10.312%	$210.5305	$210.53	$210.55	$210.50
Purchase #6	$37.71	11.788%	$42.1553	$42.16	$42.15	$42.20
Purchase #7	$245.80	7.219%	$263.5443	$263.54	$263.55	$263.50
7 purchase totals =	$1,010.49		$1,100.2140	$1,100.21	$1,100.25	$1,100.20