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	$5.97	9.149%	$6.5162	$6.52	$6.50	$6.50
Purchase #2	$117.86	4.822%	$123.5432	$123.54	$123.55	$123.50
Purchase #3	$47.75	10.465%	$52.747	$52.75	$52.75	$52.70
Purchase #4	$115.25	4.557%	$120.5019	$120.50	$120.50	$120.50
Purchase #5	$67.83	4.862%	$71.1279	$71.13	$71.15	$71.10
Purchase #6	$80.81	10.658%	$89.4227	$89.42	$89.40	$89.40
Purchase #7	$177.95	7.534%	$191.3568	$191.36	$191.35	$191.40
7 purchase totals =	$613.42		$655.2157	$655.22	$655.20	$655.10