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	$207.86	11.455%	$231.6704	$231.67	$231.65	$231.70
Purchase #2	$164.77	6.122%	$174.8572	$174.86	$174.85	$174.90
Purchase #3	$73.25	12.422%	$82.3491	$82.35	$82.35	$82.30
Purchase #4	$67.81	5.870%	$71.7904	$71.79	$71.80	$71.80
Purchase #5	$63.75	10.303%	$70.3182	$70.32	$70.30	$70.30
Purchase #6	$201.69	13.401%	$228.7185	$228.72	$228.70	$228.70
Purchase #7	$71.83	11.452%	$80.056	$80.06	$80.05	$80.10
7 purchase totals =	$850.96		$939.7598	$939.77	$939.70	$939.80