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	$135.98	3.597%	$140.8712	$140.87	$140.85	$140.90
Purchase #2	$223.89	4.383%	$233.7031	$233.70	$233.70	$233.70
Purchase #3	$171.47	8.441%	$185.9438	$185.94	$185.95	$185.90
Purchase #4	$34.83	10.805%	$38.5934	$38.59	$38.60	$38.60
Purchase #5	$13.95	11.802%	$15.5964	$15.60	$15.60	$15.60
Purchase #6	$93.72	10.380%	$103.4481	$103.45	$103.45	$103.40
Purchase #7	$145.82	10.665%	$161.3717	$161.37	$161.35	$161.40
7 purchase totals =	$819.66		$879.5277	$879.52	$879.50	$879.50