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	$46.73	10.288%	$51.5376	$51.54	$51.55	$51.50
Purchase #2	$50.50	11.749%	$56.4332	$56.43	$56.45	$56.40
Purchase #3	$69.40	12.818%	$78.2957	$78.30	$78.30	$78.30
Purchase #4	$85.57	4.425%	$89.3565	$89.36	$89.35	$89.40
Purchase #5	$221.34	13.208%	$250.5746	$250.57	$250.55	$250.60
Purchase #6	$13.35	4.533%	$13.9552	$13.96	$13.95	$14.00
Purchase #7	$40.51	13.340%	$45.914	$45.91	$45.90	$45.90
7 purchase totals =	$527.40		$586.0668	$586.07	$586.05	$586.10