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	$104.74	6.459%	$111.5052	$111.51	$111.50	$111.50
Purchase #2	$123.39	5.707%	$130.4319	$130.43	$130.45	$130.40
Purchase #3	$249.48	9.629%	$273.5024	$273.50	$273.50	$273.50
Purchase #4	$234.80	4.189%	$244.6358	$244.64	$244.65	$244.60
Purchase #5	$127.38	3.819%	$132.2446	$132.24	$132.25	$132.20
Purchase #6	$185.99	6.717%	$198.4829	$198.48	$198.50	$198.50
Purchase #7	$84.34	7.143%	$90.3644	$90.36	$90.35	$90.40
7 purchase totals =	$1,110.12		$1,181.1672	$1,181.16	$1,181.20	$1,181.10