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	$249.85	6.604%	$266.3501	$266.35	$266.35	$266.40
Purchase #2	$42.50	4.645%	$44.4741	$44.47	$44.45	$44.50
Purchase #3	$93.91	7.805%	$101.2397	$101.24	$101.25	$101.20
Purchase #4	$71.25	10.763%	$78.9186	$78.92	$78.90	$78.90
Purchase #5	$36.47	3.343%	$37.6892	$37.69	$37.70	$37.70
Purchase #6	$21.33	10.193%	$23.5042	$23.50	$23.50	$23.50
Purchase #7	$182.60	7.439%	$196.1836	$196.18	$196.20	$196.20
7 purchase totals =	$697.91		$748.3595	$748.35	$748.35	$748.40