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	$7.50	10.705%	$8.3029	$8.30	$8.30	$8.30
Purchase #2	$126.40	10.148%	$139.2271	$139.23	$139.25	$139.20
Purchase #3	$52.61	3.141%	$54.2625	$54.26	$54.25	$54.30
Purchase #4	$208.61	13.497%	$236.7661	$236.77	$236.75	$236.80
Purchase #5	$238.95	10.414%	$263.8343	$263.83	$263.85	$263.80
Purchase #6	$127.32	10.226%	$140.3397	$140.34	$140.35	$140.30
Purchase #7	$227.46	12.828%	$256.6386	$256.64	$256.65	$256.60
7 purchase totals =	$988.85		$1,099.3712	$1,099.37	$1,099.40	$1,099.30