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	$217.34	12.213%	$243.8837	$243.88	$243.90	$243.90
Purchase #2	$81.74	5.621%	$86.3346	$86.33	$86.35	$86.30
Purchase #3	$19.94	3.363%	$20.6106	$20.61	$20.60	$20.60
Purchase #4	$168.72	10.749%	$186.8557	$186.86	$186.85	$186.90
Purchase #5	$22.69	6.164%	$24.0886	$24.09	$24.10	$24.10
Purchase #6	$16.35	12.230%	$18.3496	$18.35	$18.35	$18.30
Purchase #7	$39.92	5.779%	$42.227	$42.23	$42.25	$42.20
7 purchase totals =	$566.70		$622.3498	$622.35	$622.40	$622.30