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	$17.82	13.734%	$20.2674	$20.27	$20.25	$20.30
Purchase #2	$20.40	7.337%	$21.8967	$21.90	$21.90	$21.90
Purchase #3	$88.28	9.117%	$96.3285	$96.33	$96.35	$96.30
Purchase #4	$68.27	4.478%	$71.3271	$71.33	$71.35	$71.30
Purchase #5	$26.29	10.837%	$29.139	$29.14	$29.15	$29.10
Purchase #6	$227.34	12.303%	$255.3096	$255.31	$255.30	$255.30
Purchase #7	$218.57	7.172%	$234.2458	$234.25	$234.25	$234.20
7 purchase totals =	$666.97		$728.5141	$728.53	$728.55	$728.40