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	$246.27	10.120%	$271.1925	$271.19	$271.20	$271.20
Purchase #2	$76.58	3.561%	$79.307	$79.31	$79.30	$79.30
Purchase #3	$52.56	12.704%	$59.2372	$59.24	$59.25	$59.20
Purchase #4	$81.27	12.479%	$91.4117	$91.41	$91.40	$91.40
Purchase #5	$15.40	9.721%	$16.897	$16.90	$16.90	$16.90
Purchase #6	$231.40	12.155%	$259.5267	$259.53	$259.55	$259.50
Purchase #7	$104.68	6.329%	$111.3052	$111.31	$111.30	$111.30
7 purchase totals =	$808.16		$888.8773	$888.89	$888.90	$888.80