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	$98.71	13.564%	$112.099	$112.10	$112.10	$112.10
Purchase #2	$158.28	10.176%	$174.3866	$174.39	$174.40	$174.40
Purchase #3	$36.32	3.283%	$37.5124	$37.51	$37.50	$37.50
Purchase #4	$98.34	6.192%	$104.4292	$104.43	$104.45	$104.40
Purchase #5	$31.39	6.606%	$33.4636	$33.46	$33.45	$33.50
Purchase #6	$44.51	10.802%	$49.318	$49.32	$49.30	$49.30
Purchase #7	$44.36	12.205%	$49.7741	$49.77	$49.75	$49.80
7 purchase totals =	$511.91		$560.9829	$560.98	$560.95	$561.00