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	$138.65	7.668%	$149.2817	$149.28	$149.30	$149.30
Purchase #2	$176.41	6.648%	$188.1377	$188.14	$188.15	$188.10
Purchase #3	$61.57	9.473%	$67.4025	$67.40	$67.40	$67.40
Purchase #4	$102.86	13.157%	$116.3933	$116.39	$116.40	$116.40
Purchase #5	$192.34	13.514%	$218.3328	$218.33	$218.35	$218.30
Purchase #6	$43.55	9.715%	$47.7809	$47.78	$47.80	$47.80
Purchase #7	$84.92	5.823%	$89.8649	$89.86	$89.85	$89.90
7 purchase totals =	$800.30		$877.1938	$877.18	$877.25	$877.20