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	$92.25	6.557%	$98.2988	$98.30	$98.30	$98.30
Purchase #2	$246.69	13.273%	$279.4332	$279.43	$279.45	$279.40
Purchase #3	$47.80	13.267%	$54.1416	$54.14	$54.15	$54.10
Purchase #4	$197.76	4.774%	$207.2011	$207.20	$207.20	$207.20
Purchase #5	$198.95	10.511%	$219.8616	$219.86	$219.85	$219.90
Purchase #6	$50.51	5.473%	$53.2744	$53.27	$53.25	$53.30
Purchase #7	$56.37	5.698%	$59.582	$59.58	$59.60	$59.60
7 purchase totals =	$890.33		$971.7927	$971.78	$971.80	$971.80