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	$39.96	7.342%	$42.8939	$42.89	$42.90	$42.90
Purchase #2	$213.48	12.219%	$239.5651	$239.57	$239.55	$239.60
Purchase #3	$183.70	6.848%	$196.2798	$196.28	$196.30	$196.30
Purchase #4	$44.77	4.760%	$46.9011	$46.90	$46.90	$46.90
Purchase #5	$162.90	4.605%	$170.4015	$170.40	$170.40	$170.40
Purchase #6	$95.37	9.678%	$104.5999	$104.60	$104.60	$104.60
Purchase #7	$21.74	11.157%	$24.1655	$24.17	$24.15	$24.20
7 purchase totals =	$761.92		$824.8068	$824.81	$824.80	$824.90