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	$138.73	6.117%	$147.2161	$147.22	$147.20	$147.20
Purchase #2	$111.43	11.787%	$124.5643	$124.56	$124.55	$124.60
Purchase #3	$6.87	9.740%	$7.5391	$7.54	$7.55	$7.50
Purchase #4	$78.59	13.357%	$89.0873	$89.09	$89.10	$89.10
Purchase #5	$64.26	9.145%	$70.1366	$70.14	$70.15	$70.10
Purchase #6	$86.70	13.240%	$98.1791	$98.18	$98.20	$98.20
Purchase #7	$63.77	9.853%	$70.0533	$70.05	$70.05	$70.10
7 purchase totals =	$550.35		$606.7758	$606.78	$606.80	$606.80