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	$81.39	12.664%	$91.6972	$91.70	$91.70	$91.70
Purchase #2	$196.57	7.224%	$210.7702	$210.77	$210.75	$210.80
Purchase #3	$186.55	3.426%	$192.9412	$192.94	$192.95	$192.90
Purchase #4	$45.28	5.387%	$47.7192	$47.72	$47.70	$47.70
Purchase #5	$83.52	10.759%	$92.5059	$92.51	$92.50	$92.50
Purchase #6	$74.91	6.146%	$79.514	$79.51	$79.50	$79.50
Purchase #7	$90.44	9.803%	$99.3058	$99.31	$99.30	$99.30
7 purchase totals =	$758.66		$814.4535	$814.46	$814.40	$814.40