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	$48.56	6.711%	$51.8189	$51.82	$51.80	$51.80
Purchase #2	$148.72	10.446%	$164.2553	$164.26	$164.25	$164.30
Purchase #3	$223.98	6.419%	$238.3573	$238.36	$238.35	$238.40
Purchase #4	$164.90	12.564%	$185.618	$185.62	$185.60	$185.60
Purchase #5	$212.33	7.638%	$228.5478	$228.55	$228.55	$228.50
Purchase #6	$15.42	4.241%	$16.074	$16.07	$16.05	$16.10
Purchase #7	$27.43	6.250%	$29.1444	$29.14	$29.15	$29.10
7 purchase totals =	$841.34		$913.8157	$913.82	$913.75	$913.80