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	$96.51	7.354%	$103.6073	$103.61	$103.60	$103.60
Purchase #2	$244.97	11.797%	$273.8691	$273.87	$273.85	$273.90
Purchase #3	$38.73	5.131%	$40.7172	$40.72	$40.70	$40.70
Purchase #4	$106.89	4.725%	$111.9406	$111.94	$111.95	$111.90
Purchase #5	$89.46	9.810%	$98.236	$98.24	$98.25	$98.20
Purchase #6	$82.69	12.103%	$92.698	$92.70	$92.70	$92.70
Purchase #7	$65.50	11.172%	$72.8177	$72.82	$72.80	$72.80
7 purchase totals =	$724.75		$793.8859	$793.90	$793.85	$793.80