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	$123.59	3.691%	$128.1517	$128.15	$128.15	$128.20
Purchase #2	$231.66	8.527%	$251.4136	$251.41	$251.40	$251.40
Purchase #3	$143.76	7.339%	$154.3105	$154.31	$154.30	$154.30
Purchase #4	$110.35	7.646%	$118.7874	$118.79	$118.80	$118.80
Purchase #5	$107.27	3.715%	$111.2551	$111.26	$111.25	$111.30
Purchase #6	$168.87	3.119%	$174.1371	$174.14	$174.15	$174.10
Purchase #7	$206.81	3.616%	$214.2882	$214.29	$214.30	$214.30
7 purchase totals =	$1,092.31		$1,152.3436	$1,152.35	$1,152.35	$1,152.40