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	$100.99	7.421%	$108.4845	$108.48	$108.50	$108.50
Purchase #2	$81.88	5.478%	$86.3654	$86.37	$86.35	$86.40
Purchase #3	$215.85	5.233%	$227.1454	$227.15	$227.15	$227.10
Purchase #4	$108.43	5.339%	$114.2191	$114.22	$114.20	$114.20
Purchase #5	$55.55	6.643%	$59.2402	$59.24	$59.25	$59.20
Purchase #6	$17.55	7.459%	$18.8591	$18.86	$18.85	$18.90
Purchase #7	$80.32	10.739%	$88.9456	$88.95	$88.95	$88.90
7 purchase totals =	$660.57		$703.2593	$703.27	$703.25	$703.20