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	$51.32	13.682%	$58.3416	$58.34	$58.35	$58.30
Purchase #2	$94.53	5.102%	$99.3529	$99.35	$99.35	$99.40
Purchase #3	$106.81	13.122%	$120.8256	$120.83	$120.85	$120.80
Purchase #4	$53.67	7.160%	$57.5128	$57.51	$57.50	$57.50
Purchase #5	$249.58	3.732%	$258.8943	$258.89	$258.90	$258.90
Purchase #6	$142.77	3.602%	$147.9126	$147.91	$147.90	$147.90
Purchase #7	$33.95	4.734%	$35.5572	$35.56	$35.55	$35.60
7 purchase totals =	$732.63		$778.3970	$778.39	$778.40	$778.40