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	$64.32	11.718%	$71.857	$71.86	$71.85	$71.90
Purchase #2	$111.98	4.525%	$117.0471	$117.05	$117.05	$117.00
Purchase #3	$103.73	7.828%	$111.85	$111.85	$111.85	$111.90
Purchase #4	$55.43	4.119%	$57.7132	$57.71	$57.70	$57.70
Purchase #5	$141.61	8.460%	$153.5902	$153.59	$153.60	$153.60
Purchase #6	$242.45	12.619%	$273.0448	$273.04	$273.05	$273.00
Purchase #7	$189.54	3.244%	$195.6887	$195.69	$195.70	$195.70
7 purchase totals =	$909.06		$980.7910	$980.79	$980.80	$980.80