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	$45.34	10.523%	$50.1111	$50.11	$50.10	$50.10
Purchase #2	$27.86	11.580%	$31.0862	$31.09	$31.10	$31.10
Purchase #3	$165.72	12.860%	$187.0316	$187.03	$187.05	$187.00
Purchase #4	$57.57	7.533%	$61.9067	$61.91	$61.90	$61.90
Purchase #5	$24.57	4.110%	$25.5798	$25.58	$25.60	$25.60
Purchase #6	$170.52	12.577%	$191.9663	$191.97	$191.95	$192.00
Purchase #7	$237.32	10.726%	$262.7749	$262.77	$262.75	$262.80
7 purchase totals =	$728.90		$810.4566	$810.46	$810.45	$810.50